Question 754382
Using Pythagoras
 Hypotenuse = (x + 6)
 Longer leg = (x + 3)
 Short leg = x

Therefore x^2 + (x + 3)^2 = (x + 6)^2
         x^2 + (x^2 + 6x + 9) = (x^2 + 12x + 36)
             2x^2 + 6x + 9  = x^2 + 12x + 36
             2x^2 - x^2 + 6x - 12x + 9 - 36 + 0
                  x^2 - 6x - 27 = 0
                  (x + 3)(x - 9)+ 0
        Therefore x = -3 (No answer)
                  x = 9

      Short leg = 9cm

     Hypotenuse^2 = Longer leg^2 + short leg^2
          (9 + 6)^2 = (9 + 3)^2 + 9^2
             15^2   =  12^2 + 9^2
              225   =  144 + 81
              225   = 225  Proved

Hope this helps
:-)