Linear regression

Little help please:

A golf club manufacturer is trying to determine how the price of a set of clubs
affects the demand for clubs. Below contains the price of a set of clubs and the monthly sales.
a) Assume the only factor influencing monthly sales is price. Fit the following
three curves to these data: linear (Y=a+bX), exponential (Y=ab^X), and multiplicative
(Y=aX^b). Which equation fits the data best based on R^2? (You should also comment on the residual plot of each model.)
b) Interpret your best-fitting equation
Price Demand
$400 20,000
$420 19,000
$440 17,000
$460 16,000
$500 14,000
$380 22,000
$290 31,000
$340 26,000
$220 41,000
$700 6,000