A bird was sitting 3 meters from the base of an oak tree and flew 5 meters to reach the top of the tree. How tall is the tree?

Pls! does anybody know a shortcut for answering these types of questions in the future?

How many liters of peroxide should be added to 12 liters of an 8% peroxide solution so that the resulting solution contains 16% peroxide?   original added new amount of peroxide 0.96 liters x 0.96 + x amount of solution 12 liters x 12 + x 0.18 liter 1.14 liters 1.92 liters 2.10 liters

Can someone me immediately, this is due by midnight! if you can't see the question, i'll text it to you. show the steps you took to get your answer.