3.5X＋1.8＝12.3
3.5X=12.3-1.8
3.5X=10.5
X=10.5/3.5
X=3
3.6X÷2＝2.16
3.6X=2*2.16
3.6X=4.32
X=4.32/3.6
X=1.2
x ×(16+38)=1312
54X=1312
X=1312/54
X=656/27