4X-24=2X+20
2X=44
X=22
2X（X-0.7）=4.8
2X²-1.4X-4.8=0
X²-0.7X-2.4 =0
∵a=1.b=-0.7 c=-2.4,
Δ=（-0.7）²-4×1×（-2.4）=14.5＞0
X1=（0.7+√14.5）／2×1=（0.7+√14.5）／2,
X2=（0.7-√14.5）／2×1=（0.7-√14.5）／2,
0.6X+3X2.5=67.5
8.1X=67.5
X=225／27
（X-7）除以3=8
X-7=24
X=31
5X-1.5X8=0 0.375
5X=12.0375
X=2.4075
X8-7X=0.2 4
X=0.24
（X+0.2）=1.2