How to find $\mathbb{E}(V)$ where $V = \frac{100}{2^X}$ and $X\sim \Gamma(3,1)$.

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How would I compute this? I tried doing: $$ \mathbb{E}(V) = \mathbb{E}(\mathbb{E}(V|X)) = \mathbb{E} (\mathbb{E}(\frac{100}{2^X}|X=x)) $$ but that seems to not help at all... since doesn't the inner expectation just become $100/2^X$?