90 − (15 + 9) : 8;
18 + 9 * (13 − 7);
64 − (28 + 4) : 4;
72 : 9 + 2 * 7;
9 * 6 − 30 : 3;
28 : 7 + 5 * 6;
☐ * 8 = 56;
6 * ☐ = 54;
☐ * 9 = 63.
90 − (15 + 9) : 8 = 90 − 24 : 8 = 90 − 3 = 87
18 + 9 * (13 − 7) = 18 + 9 * 6 = 18 + 9 * 6 = 18 + 54 = 72
64 − (28 + 4) : 4 = 64 − 32 : 4 = 64 − 8 = 56
72 : 9 + 2 * 7 = 8 + 14 = 22
9 * 6 − 30 : 3 = 54 − 10 = 44
28 : 7 + 5 * 6 = 4 + 30 = 34
☐ * 8 = 56
☐ = 56 : 8
☐ = 7
7 * 8 = 56
6 * ☐ = 54
☐ = 54 : 6
☐ = 9
6 * 9 = 54
☐ * 9 = 63
☐ = 63 : 9
☐ = 7
7 * 9 = 63