Ответ:
1)120+x*3=375
x*3=375-120
x*3=255
x=3_/255
2)24000/(x-12)=80 |*(x-12)
24000=80(x-12)
24000=80x-12*80
24000=80x-960
80x=24000+960
80x=24960
x=24960/80
x=312
12
*
80
------
960
3)x/26+1654=2610
x/26=2610-1654
x/26=956 |*26
x=956*26
x=24856
2610
-
1654
---------
956