Ask yourself what do I have to multiply one by to get three ( the answer is three) Because one side is multiplied by three, you have to multiply the right hand side by three to get y 3*3 is 9
Therefore, the y for 3 hours is 9
Then, we have to make another ratio 1:3 = 5:x
Ask yourself what do I have to multiply by one to get five (the answer is five) So you multiply the other side by five as well 3*5=15