54:х + 11 = 800 : 40
54:х+11 = 20
54:х = 20 - 11
54:х = 9
х= 54 : 9
х=6
----------------------------
54 : 6 + 11 = 800:40
9 + 11 = 20
20=20
х*5 +12*9 = 138
5х + 108 = 138
5х = 138 - 108
5х = 30
х = 30:5
х=6
---------------------
6 * 5 + 12*9 = 138
30 +108 = 138
138=138
120 + х*3 = 375
х*3 = 375 - 120
3х = 255
х= 255 :3
х = 85
-----------------------
120 + 85 *3 =375
120 +255=375
375=375
600 - 120 +х*6 =600
6х = 600-600 + 120
6х =120
х=120:6
х= 20
--------------------------------
600 - 120 + 20*6 = 600
600 - 120 + 120 = 600
600=600
1260 +2х=3000
2х = 3000 - 1260
2х =1740
х=1740 :2
х= 870
---------------------------
1260 + 2*870 = 3000
1260 +1740=3000
3000=3000