1.7x+2.5x=12.6
4.2x=12.6
x=12.6÷4.2
x=3
5x-4.2=8.8
5x=8.8+4.2
5x=13
x=13÷5
x=2.6
x除于5/6=1/4
x=1/4×5/6
x=5/24