To find the percentage change from 80 to 90, we need to first calculate the difference between the two numbers.

Step 1: Difference = Final Value - Initial Value

Difference = 90 - 80

Difference = 10

Step 2: Next, we need to find the absolute value of the difference. This is because percentage change is always calculated as a positive value.

Absolute Difference = |Difference|

Absolute Difference = |10|

Absolute Difference = 10

Step 3: Now, we can calculate the percentage change using the formula:

Percentage Change = (Absolute Difference / Initial Value) x 100

Percentage Change = (10 / 80) x 100

Percentage Change = 12.5%

Therefore, the percentage change from 80 to 90 is 12.5%. This means that there was an increase of 12.5% from 80 to 90.