2.8x4-5x=5.8
11.2-5X=5.8
5X=11.2-5.8
5X=5.4
X=1.08
1.6x+2.4=7.2
解1.6X=7.2-2.4
1.6X=4.8
X=3
3.4x-6=4.2
解3.4X=4.2+6
3.4X=10.2
X=3
7.8x+5=44
解7.8X=44-5
7.8X=39
X=5