(700:a+20)-60=100,
700:a+20=100+60
700:a+20=160
700:a=160-20
700:a=140
a=140:700
a=0,5
(3*a-20)+50=300,
3a-20=300-50
3a-20=250
3a=250+20
3a=270
a=270:3
a=90
(y:4-35)*12=300,
y:4-35=300:12
y:4-35=25
y:4=25+35
y:4=60
y=60*4
y=240
(150:y+6)-6=50
150:y+6-6=50
150:y=50
y=150:50
y=3