[(x + 90) × 5 + 700] : 600 = 2
[(x + 90) × 5 + 700] = 2 × 600
(x + 90) × 5 + 700 = 1200
(x + 90) × 5 = 1200 - 700
(x + 90) × 5 = 500
x + 90 = 500 : 5
x + 90 = 100
x = 100 - 90
x = 10