33.3 because 27/50=36/x and x=66.67 and thats how much as decayed after 36 hours but you want what is left so subtract from 100 and get 33.3
4 houses in 3 days
4 x 5 houses in 3 x 5 days
20 hosues in 15 days
-4x^4 - 15x^2 + 1 - 19/x^2 is your answer
Hope I helped :)
