Hello!
Part 1
To find the percentage you divide the new price by the old one
15 / 5 = 3
Convert it into a percent
3 = 300%
The answer is a 300% increase
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Part 2
Do the same thing we did in part one divide the new price by the old
5 / 15 = 0.33...
Convert into a percent
0.33 = 33%
The answer is a 33% decrease
Hope this helps!