Puzzle ZHRW 

Workings

Hint
The number is less than 100.

Answer
4.

4's double is 8, and 4's quarter is 1.

Reasoning
If the missing number is N, then:

  2N = N + 7
       —
       4

Multiply throughout by 4:

  8N = N + 28

Subtract N from both sides:

  7N = 28

Divide throughout by 7:

   N = 4