They are not the same thing.
I think this is a least common multiple question
So they would all arrive on day 504, (which probably is a few years)
8 = 2 × 2 × 2
18 = 2 × 3 × 3
21 = 3 × 7
I might be right I might be wrong, IM not positively sure but yknow
6(x²-4x+4-4)+1=0, 6(x-2)²-24+1=0, 6(x-2)²=23, x-2=±√(23/6), x=2±√(23/6)=2±1.95789, so x=3.95789 or 0.04211 approx. These are the zeroes.
24 is 2% of 120. It’s not that hard