120-x=45-15
120-x=30
x=120-30
x= 90
120-x+15=45
120-x =45-15
120-x =30
x =120-30
x =90
120-X+15=45
[120+15]-X=45
135-X=45
X=135-45
X=90
120-x+15=45
120-x=45-15
120-x=30
x=120-30
x=90
<=>x+15=120-45
=>x+25=75
=>x=75-25
=>x=50
120 -ích=45-15
120-ích=30
ích=120-30
ích=90