Scalar resolute to find an unknown component

Let $\tvec{u} = a\tvec{i} - 3\tvec{j} + 5\tvec{k}$, where $a \in R$, and $\tvec{v} = 2\tvec{i} - 2\tvec{j} - \tvec{k}$.

If the scalar resolute of $\tvec{u}$ in the direction of $\tvec{v}$ is 2, then the value of $a$ is