What is the missing constant term in the perfect square that starts with x^2+6x ?

How do i do this activity, is appreciated

The perimeter of a movie screen is 54 meters. the screen is 18 meters wide. how tall is it?

My math teacher told my class to "steal" a 6th grade fraction word problem from the internet, word problems? : -p requirements: only a 1 step word problem. needs to be complex.