Please help guys. my teacher was gonna help me with these but corona has school cancelled obviously

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?

Agallon of apple juice cost $7 a pack of eight 4.23oz box of apple juice $2.39 which is a better deal

Ithink i know it but i want to be sure so can you me out ?