Find x (Type the number answer)

Aparallelogram has two side lengths of 5 units. three of its sides have equations y = 0, y = 2, y = 2x. find the equation of the fourth side.

How to do this , and can some one explain

If f(x) = 4 - x2 and g(x) = 6x, which expression is equivalent to (g-f)(3)? 06-3-(4 + 3)2 06-3-(4-33 6(3) - 4 +32 6(3) -4 -32