The highest common factor is 3 because 9 doesn't go into 123, so 3 is on the outside of the bracket like 3(_____). To get from 3 to 9x, you multiply by 3x, which is the first term in the brackets. To get from 3 to 123y, you multiply by 41y, the second term in the brackets. Your answer is therefore 3(3x + 41y). I hope this helps!