Explanation:

To find the percent increase:

- We start with 90 and it becomes 117.

- The increase is $117-90=27$.

- To find the percentage increase, use the formula: $(\frac{\text{increase}}{\text{original number}})\times 100$.

- This gives $(\frac{27}{90})\times 100=30$.

Let's evaluate the options:

- Option 1: 20 - This would mean an increase of $18$ (since $(\frac{20}{100})\times 90=18$), but 90 + 18 is not 117.

- Option 2: 30 - This is the correct one since $(\frac{30}{100})\times 90=27$, and 90 + 27 = 117.

- Option 3: 15 - This would mean an increase of $13.5$ $(\frac{15}{100})\times 90$, which doesn’t add up.

- Option 4: 25 - An increase of $22.5$ $(\frac{25}{100})\times 90$ also doesn’t suffice.

The correct answer is:

- Option 2: 30