Answer
$3\sqrt[]{a-1}$
Work Step by Step
Simplifying each term and then combining like terms, the given expression, $
\sqrt[]{4a-4}+\sqrt[]{a-1}
,$ is equivalent to
\begin{array}{l}\require{cancel}
\sqrt[]{4\cdot(a-1)}+\sqrt[]{a-1}
\\\\=
\sqrt[]{(2)^2\cdot(a-1)}+\sqrt[]{a-1}
\\\\=
2\sqrt[]{a-1}+\sqrt[]{a-1}
\\\\=
3\sqrt[]{a-1}
.\end{array}
* Note that it is assumed that all variables represent positive numbers.