The Grand Canyon Skywalk at Eagle Point is a horseshoe shaped steel frame with glass floor looking down to the Grand Canyon below.The Skywalk extends 70 feet over the canyon rim and is 10 feet wide.The walkway consists of a semicircle with a straight portion on each side as indicated in the diagram below.

1. [5 pts] In order to prevent anyone from falling over the sides, a new railing needs to be installed.How many linear feet of railing are needed to line both sides of the walkway?(Round your final answer to 1 decimal place and any intermediate calculations to 2 decimal places.Be sure to include units.)

I am not sure where to start this problem... I unlocked the answer on here but i'm not sure where the circumference answer is coming from...