daniel has $50 saved and makes $7.50 per hour working how much money would daniel have after working 10 hours

What is the first step of an indirect proof of a number that is divisible by two

Ineed in figuring out this problem.

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?