15.6+2.3=19.69
17.9 х=19.69
х=19.69:17.9
х=1,1
1/6:(1/4х-1/3)-3/8=1/40
1/6:(1/4х-1/3)=1/40+3/8
1/6:(1/4х-1/3)=1/40+15/40
1/6:(1/4х-1/3)=2/5
1/4х-1/3=1/6:2/5
1/4х-1/3=5/12
1/4х=5/12+1/3
1/4х=5/12+4/12
1/4х=9/12
х=9/12:1/4
<span>х=3</span>
Х×9-15=66
Х×9=66+15
Х×9=81
Х=81:9
Х=9
Проверка:
9×9-15=66
81-15=66