Please I need help urgently

Another type of subtraction equation is 16-b=7. explain how you would sole this equation then solve it.

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.

What is the sum of these mixed numbers 4 2/3+ 3 1/9