A)d÷30=200-80 б)140-x=630÷7 в)6×c=420+120 г)320÷a=72÷36

D÷30=200-80
d : 30 = 120
d = 120 * 30
d = 3 600
___________
3 600 : 30 = 200 - 80
 
140-x=630÷7
140 - х = 90
х = 140 - 90
х = 50
__________
140 - 50 = 630 : 7
6×c=420+120
6×c = 540
с = 540 : 6
с = 90
__________
6 * 90 = 420 + 120
320÷a=72÷36
320÷a = 2
а = 320 : 2
а = 160
__________
320 : 160 = 72 : 36