Adiver starts at 5m and changes -16m

Element x decays radioactively with a half life of 8 minutes. if there are 450 grams of element x, how long, to the nearest tenth of a minute, would it take the element to decay to 37 grams?

The bottom of a vase is a square.each side measury y+11 units.the square has a perimeter of 55 units what is the value of y?

Me because i don't understand how to do it.: )