I would say 3 because terms are separated by a plus or minus sign and there are 2 subtraction signs separating 3 expressions.
21= 1,3,7,21
30= 1,2,3,5,6,10,15,30
common factors= 1,3
Im assuming you mean 20pence? if so its 5 twenty pence in a pound so times 5 by 9 gives you 45
so there are 45 twenty pence in £9
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