e = [( 524 - 16 × 7 : 4 ) + 504 ] : 10 =
e = [( 524 - 112 : 4 ) + 504 ] : 10 =
e = [( 524 -28 ) + 504] : 10 =
e =( 496 + 504 ) : 10 =
e = 1000 : 10 =
e = 100
d = e x 2
d = 100 × 2
d = 200
c = d : 5
c = 200 : 5
c = 40
b = c : 2
b = 40 : 2
b = 20
a = b x 3
a = 20 x 3
a = 60