What is the solution to this system of linear equations?

x + y = 4

x − y = 6

(4, 6)
(6, 4)
(5, −1)
(−1, 5)

Suppose that the price p, in dollars, and the number of sales, x, of a certain item follow the equation 4 p plus 4 x plus 2 pxequals56. suppose also that p and x are both functions of time, measured in days. find the rate at which x is changing when xequals2, pequals6, and startfraction dp over dt endfraction equals1.5.