Ta có \(\frac{23+n}{40+n}=\frac{3}{4}\)
\(\Rightarrow\left(23+n\right)\times4=\left(40+n\right)\times3\)
\(\Rightarrow92+4n=120+3n\)
\(\Rightarrow4n-3n=120-92\)
\(\Rightarrow1n=28\)
\(\Rightarrow x=28\in Z\)
Vậy x = 28
Thank you, cảm ơn bạn rất nhiều!!!!!!!!!!!!!!!!!