So we have the function in two variables. C equals 40 d plus 400.15 m, and what this function is representing is the cost C of renting a car for D days and traveling and Miles. Um So, for example, if we have the, um Value or the argument f of three comma 200 we could just input three and 200 as the values off D and M's, this becomes 40 times three plus 0.15 times 200 40 times three is 1 20 plus 0.15 times 200 is just 30 which equals $150. So what this is saying is if you rent a car for three days and you drive 200 miles, then it will cost you $150 More generally, if we have the function f of three com a. M, we can do the same thing. We can substitute three and for D, and we just have 15.15 m. This is the same thing as 1 20 plus 0.15 m equals cost. If we see this equation, here is just a linear function in one variable where 120 is the why intercept 1200.15 is a slope. M is the independent variable and C is the dependent variable. So if we make a coordinate plain, um, where we have, um, the X and Y axes or the M and C axes, then we can grab this linear function. So we'll call this, um m and the sea. So if m increases by 100 that's our scale on the M axis and on the sea access, um, it increases by 25 hums. That's 5100 1 50 So if we graph this, um, why intercept is 120? So that's around, um, here and the slope this 0.15 which means that if you increase em, if you increase the number of miles by one, the cost will increase by 15 cents, or because our scale of the M axis is 100. If you increase in by 100 the cost increases by 15. So if this is 1 20 if m is 100 than that becomes 1 35 um, just a little bit higher and is 200 then that becomes 1 50 Um, if M is 300 than that becomes, um, 1 65 And you keep going until you have this linear function, which is just 1 20 plus 0.15 a M equals C. And what this is just representing is the cost of renting the car. Um, if you know that your only renting it for three days similarly, you can have a function of, um, de instead of em where m is 100. So in that case, you have 40 d plus 0.15 times 100 is just 15. So if we graph that function, um, then you have, um Then you have, um, a another linear equation Where in this case, um, the independent variable is days and the dependent variable is still cost. Um, so we know we can say that days are increasing by scale of one. And, um, will say this is increasing by 20 dollars. So we know the Y intercept is 15. Um, so that is around rate here. And for every, um, day, we add, because of slope is 40 for every one day, the cost increases by 40 dollars. So when d is equal toe one, we have 40 plus 15 was gonna be 55. So it's around up here when d is too. We have 80 plus 15. Um, so we have to add another 40 to 55. That becomes 95. Um, around up there, when we have d equals three, we have to add another 40 to 95 that becomes 1 35 sets around up there and we get, um, a rough sketch of the line 40 D plus 15 equals C. And just like the last graph, this is just a linear equation where if we hold the miles constant as 100 miles and you increase the number of days by one on the cost increases by 40 because that is a slope.