What is 8x + 5x. this is an algbraic question

If f(x)=2x-6 and g(x)=3x+9, find (f-g)(x)

Describe the 2 algebraic methods you can use to find the zeros of the function f(t)=-16t^2+400.

The area of a rectangle is 10 cm^2. one side of the rectangle is x cm. express the perimeter of the rectangle in terms of x and show that this rectangle cannot have a perimeter of 12 cm. the perimeter of the rectangle in terms of x is __ cm