下了一半:(3a-b)/2上车了:(8a-5b)-(3a-b)/2 =(16a-10b)/2-(3a-b)/2 =(16a-10b-3a+b)/2 =(13a-9b)/2人
(13a-9b)/2
1/2(13a-9b)
=8a-5b-2/3a+2/1b=找同类项=2/13a-2/9b
设上车x人3a-b-(3a-b)/2+x=8a-5bx=(13a-9b)/2