如果a:b:c=3:4:5,那么2a+3b-c\a-5b+3c 等于多少?

如果a:b:c=3:4:5,那么2a+3b-c\a-5b+3c 等于多少?
如果a:b:c=3:4:5,那么2a+3b-c\a-5b+3c 等于多少?

如果a:b:c=3:4:5,那么2a+3b-c\a-5b+3c 等于多少?
设a=3x,b=4x.c=5x
2a+3b-c\a-5b+3x=6x+12x-5x/3x-20x+15x=13x/-2x=-6.5