Final answer:
The expression 3y + 12 is factorised by taking out the common factor of 3, resulting in the factored form 3(y + 4).
Step-by-step explanation:
To factorise the expression 3y + 12, we look for a common factor that can be taken out from both terms. In this case, the common factor is 3. When we factor out the 3, we divide each term by 3 to see what is left.
The factored form of the expression is:
3(y + 4)
Here, we took the common factor of 3 and placed it outside the parentheses. What remains inside the parentheses is what we get when we divide each original term by 3. Hence, the term 'y' is unchanged, and the term '12' becomes '4' since 12 divided by 3 is 4.