\begin{align*} \text{Numerator = } & E[X^3] - 3 \mu E[X^2] + 2\mu^3\\ & = \left [ 0^3 \cdot 0.10 + 1^3 \cdot 0.25 + 2^3 \cdot 0.40 + 4^3 \cdot 0.15 + 7^3 \cdot 0.10 \right ] - 3 \cdot 2.35 \cdot 9.15 + 2 \cdot 2.35^3\\ & \approx 0 + 0.25 + 3.20 + 9.60 + 34.3 - 64.5075 + 25.96\\ & = 47.35 - 64.5075 + 25.96\\ & \approx 8.80 \end{align*}