移項更簡單吧......

15+0.75X=X

15=X-0.75X
15=X(1-0.75)
15=X(0.25)
(15/0.25)=X
(15/(25/100))=X
(15x(100/25))=X
(15x4)=X
X=60

(15+0.75x60)=60
(15+45)=60
60=60
故X=60時, 等式成立...

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