1) (7290/y)*75+100=60850
(7290/y)*75=60850-100
(7290/y)*75=60750
7290/y=60750/75
7290/y=810
y=7290/810
y=9
2) (x/12)*144-712=13688
(x/12)*144=13688+712
(x/12)*144=14400
x/12=14400/144
x/12=100
x=100*12
x=1200
3) 92/(3*b+5)=4
3*b+5=92/4
3*b+5=23
b=23-5
b=18
4) 800-(90*x+17)=423
90*x+17=800-423
90*x+17=377
90*x=377-17
90*x=360
x=360/90
x=4