194*2 =388
72*4 =288
____________
194*2=?
↓ ↓
100*2=200
90*2=180
4*2=8
200+180+8=388
_______________
72*4=?
↓ ↓
70*4=280
2*4=8
280+8=288
_________________
3*15=7(х+3)
45=7х+21
7х=45-21
7х=24
х=24/7=3 3/7
(4n + 12)÷ 8 = 136
4n + 12 = 136 × 8
4n + 12 = 1088
4n = 1088 - 12
4n = 1076
n = 1076 ÷ 4
n = 269
Проверка:
(269 × 4 + 12) ÷ 8 = 136
136 = 136