There are three basic rules that need to be understood first:
The order of operations in this case is first parentesis, then powers and finally multiplication.
When raising the product of 2 factors by a power, both factors need to be raised.
When muliplying the product of 2 factors by another factor, only 1 factor needs to be multiplied.
Starting with 3m^3 (which cannot be simplified) the first step is to square both 3 and m^3 giving 9m^6. The multiplication step only needs to be performed on one of the factors so we’ll just multiply 9 by 4 giving the result of 36m^6