（0．75x＋2）/[(1+0.75)x+2]=5/11
（0．75x＋2）/(1.75x+2)=5/11
(1.75x+2)x5=（0．75x＋2）x11
8.75x+10=8.25x+22
8.75x-8.25x=22-10
0.5x=12
x=24