So what you had done wrong on this question is that you didn't multiply by the reciprocal of 2/5, which is 5/2, not 5/1.
The steps to the solution:
Multiply 5/2 on each side: [tex] \frac{5}{2} * \frac{2}{5}x= \frac{10}{1} * \frac{5}{2} [/tex]
Then just simplify your answer: [tex]x= \frac{50}{2} =25[/tex]
