5/8+3/4*(84-x)=57
5/8+(3/4)x84-(3/4)x=57 (根据乘法分配律)
5/8+63-(3/4)x-57=57-57 (用配平法,等式两边同时加减同一个数,等式仍然成立)
5/8+6-(3/4)x=0
5/8+6-(3/4)x+(3/4)x=0+(3/4)x (用配平法)
(3/4)x = 5/8+6
x=(53/8)/ (3/4)
x=53/6
5/8+3/4*(84-x)=57
5/8+(3/4)x84-(3/4)x=57 (根据乘法分配律)
5/8+63-(3/4)x-57=57-57 (用配平法,等式两边同时加减同一个数,等式仍然成立)
5/8+6-(3/4)x=0
5/8+6-(3/4)x+(3/4)x=0+(3/4)x (用配平法)
(3/4)x = 5/8+6
x=(53/8)/ (3/4)
x=53/6