Find the sum of all values of $\theta$ such that $\theta\in[0,2\pi]$ and$$ \cos(\theta) 4\sec(\theta)

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.