a) 7+6×(X:4-18) = 25
6×(X:4-18) = 25-7
6×(X:4-18) = 18
X:4-18 = 18:6
X:4-18 = 3
X:4 = 3+18
X:4 = 21
X = 21×4
X = 84
b) 286+(a-113):5=142
(a-113):5 =142-286
(a-113):5 = -144
a - 113 = -144×5
a = -720+113
a = -607
c) [93:(x:3)-16x4]x6=186
93:(x:3)-64 = 186:6
93:(X:3)-64 = 31
93:(X:3) = 31+64
93:(X:3) = 95
X:3 = 93/95
X = 3×93/95
X= 279/95
