Theory:

When multiplying monomials, their coefficients are multiplied and the exponents of the variables (letters) are added.
Important!
Remember: anam=an+m
Example:
Multiply the monomials:
3a2b2ab3
 
1) To make the expression clearer, rearrange the factors.
3a2b2ab3=32a2a1b1b3
 
2) Multiply the coefficients and add the exponents of the variables (letters).
32a2+1b1+3=6a3b4=6a3b4