Answer:

Explanation:
When you add fractions with different denominators, you need to find the Least common denominator (LCD):
Descompose the denominators (5 and 15) into its prime factors and then choose the commons and non-commons with the highest exponents:

Divide the LCD by each original denominator of each fraction and multiply the result by each original numerator of each fraction. After this, you can add the numerators and reduce the fraction.
Then:
