Gasoline costs $1.99 per gallon. If the price per gallon increases an average of 6% per month, which function, models, the exponential growth of the pricing?
a. f(x) = 1.06(1.99)ₓ
b. f(x) = 1.99(1.06)ₓ
c. 1.99(0.06)ₓ
d. f(x) = 1.06ₓ1.99