The base of a ladder should be place 3 feet from the wall for every 5 feet of ladder length. How long a ladder is needed to safely reach 36 feet above ground?

This is a good ratio problem. First you have to have the correct information for the ratio, which means you need to know the ft above the ground. Use Pythag 3²+x²=5² when you solve you get 4. Now set up the ratio: 4/5=36/x or x = 45.