The answer would be 39/40.
1. Find the LCD of both of the fractions (LCD = 40)
2. Make the denominators the same as LCD (The LCD would be 40)
3. Simplify (24/40 + 15/40)
4. Join the denominators (24 + 15/40)
5. Simplify (39/40)
In decimal form its 0.975.