The cost of a jacket increased from $90.00 to $99.00. what is the percentage increase of the cost of the jacket?

The answer is 10%
thanks for the question 

1) find the difference $99 and $90. The difference should be $9.

2) after finding the difference, take the difference and put as a fraction over the original price of the jacket.

9/90

3) now you multiply the fraction by 100%. And your answer should be 10%.