### Theory:

Let us understand how brackets are used to expand the numbers and to do the calculation.
Example:
Consider $13×106$

$\begin{array}{l}13×106 =\left(10+3\right)×106\phantom{\rule{0.147em}{0ex}}\\ =10×106\phantom{\rule{0.147em}{0ex}}+\phantom{\rule{0.147em}{0ex}}3×106\\ =10×\left(100+6\right)+3×\left(100+6\right)\\ =1000+60\phantom{\rule{0.147em}{0ex}}+300+18\\ =1378\end{array}$

Thus, through the expansion of brackets, we can easily obtain the product of numbers in some cases.