I need help its due today

Acircle has a diameter will endpoints of (-2,8) and (6, 4). what is the center of the circle

Write an equation in point-slope form for the line through the given point that has the given slope (-2,-7); m=-3/2

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?