1)
(700*a +200)-600=1000
700a +200=1000+600
700a=1600-200
a=1400/700
a=2
2)
(7200-a*200)+2000=3400
7200-a*200 = 3400-2000
-a*200=1400-7200
a=5800/200
a=29
3)
(y/4 - 35)*120 = 3000
30y - 4200 = 3000
30y = 3000+4200
y=7200/30
y=240
4)
(50*y+160)-60=500
50y +160 = 500+60
50y+160 =560
50y = 560 -160
50y = 400
y=400/50
y = 8