Answer:
Child's age: 15.5
Parent's age: 46.5
Explanation:
Take child's age as C and parent's age as P
There are two conditions: P = 3C (parent is three times older than child), P = C + 31 (parent is 31 years older than child)
Therefore, 3C = C + 31
2C = 31
C = 31/2 = 15.5 (child's age)
P = 3C = 3 (15.5) = 46.5 (parent's age)