Theory:

Let us understand how brackets are used to expand the numbers and to do the calculation.
Example:
Consider 13×106
 
13×106=(10+3)×106=10×106+3×106=10×(100+6)+3×(100+6)=1000+60+300+18=1378
 
Thus, through the expansion of brackets, we can easily obtain the product of numbers in some cases.