5b4c5 x 6b3c2 =

5b4c5 x 6b3c2 =

$$\begin{array}{rcl} \mathbf{5b^4c^5 \cdot 6b^3c^2 }\\ &=& 5\cdot 6 b^4b^3c^5c^2\\ &=& 30 \cdot b^{4+3}\cdot c^{5+2}\\ \mathbf{5b^4c^5 \cdot 6b^3c^2 }& \mathbf{=} & \mathbf{30 b^7c^7}\\ \hline \\ \end{array}$$