Answer
$25a^{26/3}, \quad a^{25/3}$
Work Step by Step
$(a+b)^{n}=\left(\begin{array}{l}
n\\
0
\end{array}\right)a^{n}+\left(\begin{array}{l}
n\\
1
\end{array}\right)a^{n-1}b+\left(\begin{array}{l}
n\\
2
\end{array}\right)a^{n-2}b^{2}+\cdots+\left(\begin{array}{l}
n\\
n
\end{array}\right)b^{n}$
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The last two terms are with binomial coefficients $\left(\begin{array}{l}
n\\
n-1
\end{array}\right)$ and $\left(\begin{array}{l}
n\\
n
\end{array}\right)$, that is
$\left(\begin{array}{l}
25\\
24
\end{array}\right)=\left(\begin{array}{l}
25\\
25-24
\end{array}\right)=\left(\begin{array}{l}
25\\
1
\end{array}\right)=25$
and
$\left(\begin{array}{l}
25\\
25
\end{array}\right)=1$
Second-last term:
$25\cdot(a^{2/3})^{1}(a^{1/3})^{24}=20a^{(2+24)/3}=20a^{26/3}$
The last term:
$1\cdot(a^{1/3})^{25}=a^{25/3}$
