Help look at the picture

Which statement justifies why angle ebc measures 90?

Acyclist bike x distance at 10 miles per hour .and returns over the same path at 8 miles per hour.what is the cyclist average rate for the round trip in miles per hour ?

Answer asap. you begin with 1/2 scoop of ice cream. since you're hungry, you ask the vendor for 2/7 more scoops of ice cream. then, you eat 5/8 scoops. how many scoops of ice cream are left on your cone? i will mark brainliest for first correct answer.