Find the area and perimeter

Which value is not a solution of 8x^3 – 1 = 0

The holiday party will cost $160 if 8 people attend.if there are 40 people who attend the party, how much will the holiday party cost

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?