Whats the GCF of 18 and 30?

Well I don't know !
Let's figure it out:

-- The factors of  18  are  1,  2,  3,  6,  9, and 18 .

-- The factors of  30  are  1,  2,  3,  5,  6,  10,  15, and  30 .

-- The numbers that are factors of both  18  and  30  (the 'common' ones)
    are  1,  2,  3,  and  6 . 

-- The biggest one on that short list (the 'greatest common' one) is  6 .

What do you mean i don’t understand

D. i think it is the savings