1.(x-16)*5=420
5x - 80 = 420
5x = 420 + 80
5x = 500
x = 500 : 5
x = 100
2.(16+x)*20=680
320 + 20x = 680
20 x = 680 - 320
20 x = 360
x = 360 : 20
x = 18
3.(200-x)*6=1140
1200 -6x = 1140
-6x = 1140 - 1200
-6x = - 60
x = 10
4.(x+30)*110=7700
110x + 3300 = 7700
110x = 7700-3300
110x = 4400
x = 40