Final answer:
The value of 'm' in the equation is 3, solved by distributing and isolating the variable.
Step-by-step explanation:
To solve the equation 15 + 3m = 4(m + 3), first expand the right side of the equation by distributing the 4 into the parentheses, which yields 15 + 3m = 4m + 12.
Next, to isolate the variable 'm', we can subtract '3m' from both sides to get 15 = m + 12. Then, we subtract 12 from both sides to solve for 'm', resulting in m = 3.