X - Eva's age
[tex]\dfrac X5[/tex] - Eva's age divided by five
[tex]\left(\dfrac X5\right)^\big2[/tex] - Eva's age divided by five and then squared
[tex]\left(\dfrac X5\right)^\big2=\dfrac{X^2}{25}[/tex]
Answer:
John is [tex]\frac{X^2}{25}[/tex] years old now