This will probably be easier if all the times are converted to minutes.
4 hours = 4 x 60 = 240 minutes.
Delano = 3/4 hour = 3/4 x 60 = 45 minutes.
Alex = 2/3 hour = 2/3 x 60 = 40 minutes.
Jordan = 3/5 hour = 3/5 x 60 = 36 minutes.
Now lets take the 240 minutes and divide that be each of the times.
Delano: 240 / 45 = 5, remainder 15 ---> means that he made 5 signs and had 15 minutes left over.
Alex: 240 / 40 = 6, remainder 0 ---> means that he made 6 signs and had no minutes left over.
Jordan: 240 / 36 = 6, remainder 24 ---> means that he made 6 signs and had 24 minutes left over