Troy's truck has a 30 gallon gas tank and gets an average of 21 miles per gallon. write an equation to represent the amount of gas in troy' s truck after driving a certain number of miles (assuming he starts with a full tank). define your variables.

Given that Troy's truck has a 30 gallon gas tank and gets an average of 21 miles per gallon.

Let x represent the number of miles Troy's has driven and let y represent the amount of gas in Troy's truck, then the equation that represents the amount of gas, y, in troy' s truck after driving a certain number of miles, x, (assuming he starts with a full tank) is given by

y = 30 - x/21