Ok so, the first thing to do is divide 1518 by 4 because there are four girls which leaves us with 379.5 and they can’t have half of one each so we round that down to 379, which means the most they can all have if they must have same amount is 379 each. So now how many are left? Multiply 379 by 4 and you’ll get 1516 so there will be 2 left ;)
If you need me to explain better just ask