To increase a number by a certain percentage, you can use the following formula:

Increased Value = Original Value + (Original Value * Percentage Increase / 100)

Let’s calculate the increases for the given values:

a) Increase 90 by 10%:
Increased Value = 90 + (90 * 10 / 100)
Increased Value = 90 + 9
Increased Value = 99

So, when you increase 90 by 10%, you get 99.

b) Increase 75 by 25%:
Increased Value = 75 + (75 * 25 / 100)
Increased Value = 75 + 18.75
Increased Value = 93.75

When you increase 75 by 25%, you get 93.75.