6 ⋅ (57 - 48) = 6 ⋅ 9 = 54
7 ⋅ (70 - 61) = 7 ⋅ 9 = 63
81 : (45 : 5) = 81 : 9 = 9
84 : 21 + 55 : 5 = 4 + 11 = 15
60 : (135 - 120) ⋅ 10 = 60 : 15 ⋅ 10 = 4 ⋅ 10 = 40
(540 - 40) : 100 ⋅ 1 = 500 : 100 ⋅ 1 = 5 ⋅ 1 = 5