Final answer:
The common factors of 3a and 21ab are 3 and a. To find these, we listed the individual factors of each term and identified which factors appeared in both lists.
Step-by-step explanation:
The task is to find the common factors of the given terms, which are 3a and 21ab. To find common factors, you need to identify factors that are common to both terms. Factors are numbers that can divide another number without leaving a remainder.
Looking at the two terms:
21ab can be factored into 3, 7, a, and b.
3 (since both numbers include a multiple of 3)
a (since both terms include the variable a)
Therefore, the common factors of 3a and 21ab are 3 and a.