7 is C this is because if you pluge the x value into the equation and it gives you the y value associated with it for all the points, then it is the correct equation.
8 is A and this is the same principle
9 is C because b = 6h-3 and put this in the equation for a triangle and you get 1/2 (6h-3)h and put into one equation is (6h^2 - 3h)/2
