2) a)[(X-1): 100+90]:10-10=0/+10
[(X-1): 100+90]:10=10/x(ori) 10
(X-1): 100+90=100-90
(X-1):100=10/x(ori)100
X-1=1000/+1
X=1001
b) [(X+270:3)x(ori)5+100]:600=1/x(ori)600
(X+90)x(ori)5+100=600/-100
(X+90)x(ori)5=500/:5
X+90=100/-90
X=1
c) 9-(25-16):3=[18-3x(9-9)]xX
9-9:3=(18-3x0)xX
9-3=(18-0)xX
6=18xX
18xX=6
X=18:6
X=3