Explanation:
He added and subtracted the denominators. When adding/subtracting fractions, you need common denominator. Then you would only add/subtract the numerators.
So to solve it correctly, you would first find the common denominator, which for part a, it would be 3x5=15. Then rewrite both fractions s.t. 5/15 + 9/15
Then add the numerator. So 14/15