(1-7/8)x=21/40

(1-7/8)x=21/40
(1-7/8)x=21/40

(1-7/8)x=21/40
(1-7/8)x=21/40
x/ 8 = 21/40
x = 5分之 21
施主,我看你骨骼清奇,
器宇轩昂,且有慧根,
乃是万中无一的武林奇才.
潜心修习,将来必成大器,
鄙人有个小小的考验请点击在下答案旁的
"选为满意答案"

1/8x=21/40
x=21/40*8
x=21/5