Question

If a+b = 240     c+d  = 500      d-b+c =455      a+c   =215find the value for d

Answer 1

a+b = 240  ... 1  
c+d  = 500 ...2   
  d-b+c=455  ....3
   a+c   =215...4

1 - 4

a + b - a - c = b - c = 240 - 215 = 25..... 5

putting 5 in 3
d - (25) = 455

d = 480