Пошаговое объяснение:
1. 879-6•Х=153
6x = 879 - 153
6x = 726
x = 726 : 6
x = 121
2. 5Х+12•Х=289
17x = 289
x = 289:17
x = 17
3. (Х-348)+159=361
x - 348 = 361 - 159
x - 348 = 202
x = 202 = 348
x = 550
4. 48:(Х+3)=4
x + 3 = 48 : 4
x + 3 = 12
x = 12 - 3
x = 9
5. (12-Х)•9=99
12 - x = 99 : 9
12 - x = 11
x = 12 - 11
x = 1
6. 28+(48+Х)=100
28 + 48 + x = 100
76 + x = 100
x = 100 - 76
x = 24
7. (70-Х)-35=12
70 - x - 35 = 12
35 - x = 12
x = 35 - 12
x = 23
x - 8 + x = 32
2x - 8 = 32
2x = 32 + 8
2x = 40
x = 40:2
x = 20 карандашей во второй коробке
20 - 8 = 12 карандашей в первой коробке
10x•6=60х
5а•7b=35аb
8m•12n=96mn
2a•3b•4c=6ab•4c=24abc
5x•2y•5z=10xy•5z=50xyz