a-5b=7
a) x+3a-15b=29
x+3(a-5b)=29
x+3x7=29
x+21=29
x=8
b) x-123+5a-25b=137
x+5( a-5b)=137+123
x+5x7=260
x=260-35
x=225
c) x-2a+10b+17=4
x-2(a-5b)+17=4
x-2x7+17=4
x-14+17=4
x+3=4
x=1
d) 47-x+7a-35b=2a-10b+4
47-x+7(a-5b)=2(a-5b)+4
47-x+7x7=2x7+4
47-x+49=14+4
96-x=18
x=78