a × 42 + 720 - 720 : 9 = 1 060
a × 42 + 720 - 80 = 1 060
a × 42 = 1 060 + 80 - 720 → metoda mersului invers
a × 42 = 1 140 - 720
a × 42 = 420
a = 420 : 42
a = 10
100 - b : 16 + 350 : 7 = 144
100 - b : 16 + 50 = 144
100 - b : 16 = 144 - 50
100 - b : 16 = 94
b : 16 = 100 - 94
b : 16 = 6
b = 6 x 16
b = 96
E = 100 ×a - 10 × b = 100 × 10 - 10 × 96 = 1 000 - 960 = 40 → valoarea expresiei
