Apply Invariance of Age Difference

The difference between two people's ages remains strictly constant throughout their lifetimes. Hence, 5 years ago, their age difference was also $30\text{ years}$: $A_5 - S_5 = 30$

Difference $= 30\text{ years}$ always

Solve for Sunita's Age 5 Years Ago

Given $A_5 = 3 S_5$: $3 S_5 - S_5 = 302 S_5 = 30 \implies S_5 = 15\text{ years}$

$\text{Sunita} was 15 years old 5 \text{years ago}$

Calculate Present Age

$\text{Present Age of Sunita} = S_5 + 5 = 15 + 5 = 20\text{ years}$

$\text{Sunita}'s \text{present age} = 20 years$