Assuming that an exponentiation sign is missing, all you need to know is that rational exponents work like this:
[tex]a^{\frac{b}{c}}=\sqrt[c]{a^b}[/tex]
So, you have
[tex]25^{\frac{5}{2}}=\sqrt{25^5}=\sqrt{(5^2)^5}=5^5[/tex]
And similarly,
[tex]81^{\frac{7}{4}}=\sqrt[4]{25^7}=\sqrt[4]{(3^4)^7}=3^7[/tex]
