Explanation:

Let's solve this step-by-step:

1. Let the number of students who play only football be x.

2. Then, the number of students who play only cricket is 3x because it's three times the number of only football players.

3. Let the number of students who play both sports be y.

4. Total students playing cricket: 3x + y.

5. Total students playing football: x + y.

Given that the number of cricket players is twice that of football players:

3x + y = 2(x + y) 

Solving the equation: x = y

The total number of students is given as 100: 3x + x + y = 100

 4x + y = 100

Since x = y, replace y with x:

4x + x = 100

5x = 100 

x = 20

Therefore, y = 20.

So, the number of students who play both sports is:

- Correct Answer: 20