In 2003, a gallon of gas cost $1.75. In 2013 a gallon of gas cost $3.25. Write an equation to model this situation.

We can easily solve this by assuming a linear equation. The general form is:

y = m x + b

where y is the price of gas, x is the year, m is the slope or increase in price every year and b is the y-intercept

We can solve the slope by:

m = (3.25 - 1.75) / (2013 - 2003)

m = 0.15

y = 0.15 x + b

Using any pair data, we get the b:

3.25 = 0.15 (2013) + b

b = - 298.7

y = 0.15 x - 298.7