15:[11-(7×5-8×9:x:3):8+2×4]×3=3
15:[11-(35-72:X:3):8+8]×3 = 3
15:[11-(35-72:X:3):8+8] = 3:3
15:[11-(35-72:X:3):8+8] = 1
11-(35-72:X:3):8+8 = 15:1
11-(35-72:X:3):8+8 = 15
11-(35-72:X:3):8 = 15-8
11-(35-72:X:3):8 = 7
(35-72:X:3):8 = 11-7
(35-72:X:3):8 = 4
35-72:X:3 = 4×8
35-72:X:3 = 32
72:X:3 = 35-32
72:X:3 = 3
72:X = 3×3
72:X = 9
X = 72:9
X = 7