Gautam’s present age is equal to 20% of his father's age 15 years ago, and Gaurav's (brother of Gautam) present age is 60% of his father’s age 10 years ago. If the sum of Gautam’s present age and Gaurav’s present age is 31, then find their father’s present age.

A

40 years

B

50 years

C

55 years

D

45 years