There is a lot to go over here. Unfortunately it looks like you got a lot incorrect. I'll focus on two problems. Hopefully these examples below will help correct the other mistakes.
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Problem 7)
We have the starting value be 20 and the ending value be 11. Subtract the values: (end)-(start) = 11 - 20 = -9. The negative indicates we have a drop or decrease.
We'll focus on the positive version of this number, so 9. Divide this value over the starting amount 20 to get 9/20 = 0.45 = 45%
So going from 20 miles to 11 miles is a decrease of 45%
Answer to problem 7 is: 45%
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Problem 13)
An increase of 300% means we added 3 times the original amount onto the original amount.
We take 300% of 25 to get 3*25 = 75
Which is then added onto 25 to get 25+75 = 100
Answer to problem 13 is: 100