Which expression has the same value as 7 x 3/4?

a: - 21 x 3/4

b: - 21 x 3/28

c: - 21 1/4

d 21 x 1/28

You are standing next to a really big circular lake. you want to measure the diameter of the lake, but you don't want to have to swim across with a measuring tape! you decide to walk around the perimeter of the lake and measure its circumference, and find that it's 400\pi\text{ m}400? m. what is the diameter dd of the lake?