(7-x)*10+x 10x+(7-x) [(7-x)*10+x]+45=10x+(7-x)
10(7-x)+x10x+(7-x)10(7-x)+x+45=10x+(7-x)
10(7-x)+x10x+(7-x)10(7-x)+x+45=10x+7-x
( ⊙o⊙ )哇,好麻烦,不写了