2x+1<=x+5
2x-x<=5-1
x<=4
x+5<3x+4
3x-x>5-4
2x>1
x>1/2
1/2在1/2和4之间,1/2取不到,画个空心圈
-3<=2x-5<=3
加5
2<=2x<=8
除以2
1<=x<=4