How can you tell if a graph is a function or not

Plz ( true - false) all triangles have interior angles whose measure sum to 90.

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.

Solve the equation: x - 9 = -6 + 5 a. 21 b. 7 c. 14 d. 2