A) (ax2-40):23=12
(ax2-40)=12x23
ax2-40=276
ax2=276+40
ax2=316
a=316:2
a=158
b) {(a-416:4+2)x5+3}x2=1986
{(a-104+2)x5+3}=1986:2
(a-104+2)x5+3=993
(a-104+2)x5=993-3
(a-104+2)x5=990
a-104+2=990:5
a-104+2=198
a=198+104-2
a=300
c) {(a-1):100+90}:10-10=0
{(a-1):100+90}:10=10
{(a-1):100+90}=10x10
(a-1):100+90=100
(a-1):100=100-90
(a-1):100=10
a-1=10x100
a-1=1000
a=1000+1
a=1001
