There are several information's of immense importance that are already given in the question. Based on these information's the answer to the question can be easily deduced.
Let us assume the number to be = x
Then
(75/100) * x = 26
3x/4 = 26
3x = 26 * 4
3x = 104
x = 104/3
x = 34.67
The unknown number is 34.67. I hope the procedure is clear enough for you to understand. Using this procedure you can always solve similar problems without requiring any additional help from outside.