Answer:
6a
Explanation:
You can always choose the largest of the offered answers and see if that fits.
6ab +18a = 6a(b +3)
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Your general approach to a problem like this is to ...
- look at what you have
- identify the factors of each term
- note which ones are common
- find the largest common factor of any integer coefficients (It helps to know your times tables.)
Obviously, the only variable factor in the second term is "a". Since that is also a factor in the first term, that is part of the answer.
The constant 6 in the first term is also a factor of 18 in the second term, so it, too, will be part of the answer.
Then, the answer is 6a.