Explanation:

- Let's denote the present ages of A, B, and C as a, b, and c respectively.

- In five years, their ages will be a+5, b+5, and c+5.

- The ratio of their ages will be 3:5:2, so 3x, 5x, and 2x for some x.

- This gives us three equations:

1. a + 5 = 3x

2. b + 5 = 5x

3. c + 5 = 2x

- We are given that $a^2+b^2+c^2=525$.

- Substituting the values from the equations:

$(3x-5{)}^2+(5x-5{)}^2+(2x-5{)}^2=525$.

- Solving the equation gives x = 5.

- So, present age of B = 5x - 5 = 25 - 5 = 20 years.

- The present age of B is 20 years.