Find the value of $X$ to equal a percentage of a defined number

Question

I'm presented with the problem below, where $X$ and $Y$ are unknown. $$\begin{cases}X - 100,000 = Y\\(Y/X) \cdot 100 = 25\end{cases}$$ Is there any formula to figure out the value of $X$?

Answer 1

We substitute $Y$ by $X-100,000$ in the second equation

We have $$\frac{X-100,000}{X}=\frac{25}{100}$$

Multiplying X on both sides $$X-100,000=\frac{25}{100}X$$

or $$\frac{75}{100}X=100,000$$

or $$X=100,000\frac{100}{75}\approx 133,333.33 $$

Finally , $Y=X-100,000\approx 133,333.33-100,000\approx 33,333.33$