Questions 7 and 8. Please explain

$$\begin{gathered} 7. The number 5^{25}-3^{25} is divisible by \\ \left(a\right) 2 \left(b\right) 3 \left(c\right) 5 \left(d\right) 7 \\ 8. If the sum of the binomial coefficent in the expansion of {\left(x+\frac{1}{x}\right)}^n is \\ 64, then the term independent of x equal to \\ \left(a\right) 10 \left(b\right) 20 \left(c\right)40 \left(d\right) 60 \end{gathered}$$