Let
x---------> represent the number of miles Troy's has driven
y--------> represent the amount of gas in Troy's truck
we know that
the equation that represents the amount of gas, y, in troy' s truck after driving a certain number of miles, x is
where
m is the slope--------->
in this problem the slope is equal to
it's negative because the tank is going to be consumed
assuming he starts with a full tank
substitute in the formula above
therefore
the answer is
the equation