[(x:3 + 8):4 +7] x 5 - 10 = 40
[(x:3 + 8):4 + 7] x 5 = 40+10
[(x:3 + 8):4 + 7] x 5 = 50
(x:3 + 8):4 + 7 = 50:5
(x:3 + 8):4 + 7 = 10
(x:3 + 8):4 = 10-7
(x:3 + 8):4 = 3
x:3 + 8 = 3x4
x:3 + 8 = 12
x:3 = 12-8
x:3 = 4
x = 4x3
x = 12
40+10=5×[7+4÷(8+3:x)]
50÷5=7+4÷(8+3÷x)
10-7=4÷(8+3÷x)
3×4=8+3÷x
12-8=3÷x
X÷3=4
X=3×4
X=12