ANSWER
x = 2/5
EXPLANATION
We want to solve the equation below:
[tex]\frac{5}{2x}\text{ = }\frac{25}{4}[/tex]To do this, we cross multiply:
2x * 25 = 5 * 4
50x = 20
[tex]\begin{gathered} \Rightarrow\text{ x = }\frac{20}{50} \\ x\text{ = }\frac{2}{5} \end{gathered}[/tex]That is the solution.