Please could someone help me, I have no idea what these questions are about :S
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What have you tried? (Hint: if 4 is a factor of something then you can write it as z = 4*y for some integers z,y).
I have no Idea how to even do this question, how would I use z=4*y ?
Let z = 6a*10b = 3*2*a*2*5*b = 4*15*a*b = 4*y where y = 15ab.