Patricia paid $385 for 5 nights at a hotel find the unit rate

Can someone be awesome and me with : (

The suare root of 9x plus 7 plus the square rot of 2x equall to 7

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?