Let's start by declaring our varibles.
x = number of lawns Mr. Brust mowed
y = total amount of money Mr. Brust made
Let's create our equation.
y = 15x + 55
For part b, we can plug 800 in for y.
800 = 15x + 55
Subtract 55 from both sides.
745 = 15x
Divide both sides by 15
50 = x. Note, I rounded the answer to the nearest integer.
For part c, we can plug 13 in for x.
y = 15(13) + 55
Simplify the right side of the equation.
y = 250