Find the ages of brothers based on given ratio after 10 years

Question

The present ages of 3 brothers are in the proportion 3:4:5. After 10 years the sum of their ages will be 78. What are their ages now?

(a) 12, 17 and 20                                                     (c) 21, 28 and 35

(b)  15, 20 and 25                                                    (d) 24, 32 and 40