  -20 = -20
  16-36 = 25-45
  (4)  - 2(4)(9/2) = (5) - 2(5)(9/2)
   
  (4)- 2(4)(9/2) + (9/2)= (5)- 2(5)(9/2) + (9/2)
   
  (4 - 9/2) = (5 - 9/2) 
  (4 - 9/2) = (5 - 9/2) 
  (4 - 9/2) = (5 - 9/2) 
  4 = 5
  