To find the answer you need to write equivalent fractions with larger denominators. If you multiply each fraction by 3/3 then your equivalent fractions would be
3/5 × 3/3 = 9/15
4/5 × 3/3 = 12/15
Now we have two fractions that are equivalent to the original fractions and we can easily see that 2 fractions between 9/15 and 12/15 would be...
10/15 and 11/15
(10/15 can reduce to 2/3 so your answers could also be 2/3 and 11/15)