What are the answers to these two questions?

What is the value of the expression below? (81^2)^1/8

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

1. 2. ∠b and ∠y are right angles. 3.? 4.? which two statements are missing in steps 3 and 4? ∠x ≅ ∠c △abc ~ △zyx by the sas similarity theorem. ∠b ≅ ∠y △abc ~ △zyx by the sas similarity theorem. = 2 △abc ~ △zyx by the sss similarity theorem. = 2 △abc ~ △zyx by the sss similarity theorem.