The formula to find Percentage increase is :

Step 1:
Find the difference:
Final value - Initial value = 99-88 =11
Step 2:
divide the difference by initial value:
divide 11 by 88 , we get 1/8
Step 3:
Multiply the result of step 2 by 100
Multiplying 1/8 with 100 we get, 12.5
Answer : The percentage increase is 12.5 %.