help with math problems

(x^2 + 8x) = 20

x^2 + 8x-20 = 0

(x-2)(x+10) = 0      x = 2 or -10 

3.  Looks as though the entire rectangle is shaded...   I think we just want the 'ring' area

     area of big triangle   - area of smaller

      (  x+6)(2x+6)   - (2x)(x)  = ring area

     2x^2 +18x+36    - 2x^2 

            18x + 36    = ring area

 

   but   larger = 6 * smaller = 6 (2x)(x)

        6(2x)(x) - (2x)(x) = 10 x^2 = ring area too

Soooooo

18x + 36 = ring area = 10 x^2

or:

                0 =10x^2 - 18x-36    

                          quadratic formula shows  x = -1.2(throw out)   or      x = 3           so 'ring area = 10(3)^2 = 90 units^2