Digital Genius manufactures a cell phone charging pad that can fully charge any cell phone that is placed on it in 15 minutes. The analytics department determined that at a price of $109.00 each, the demand would be 5 thousand pads, and at $69.00 each, the demand would be 15 thousand pads. Based on the assumption that a linear relationship exists between price and demand, the price-demand equation is given by p(x) = -4(x) + 129

where x is the number of thousands of pads in demand. At what price point should they sell the pads to have a demand of 13 thousand pads?
A. $32.25
B. $52.00
C. $77.00
D. $29.00