You can only add fractions if they have the same denominator, which in this case is the 15 and the 5. So you can't add the 1/5 and the 4/15 together just yet because its not the same denominator. Multiply 3/3 to 1/5 to get the same denominator as 4/15, and it would become 3/15 because whatever you do to the top, you do to the top. Add them together and you get 7/15, and then add the whole 4 and you get 4 7/15
