Which expression are equal to 10^5

1. are the triangles similar and if so why? what is the value of x? show your work.

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?

If a and b are real numbers, then |a-b| is always, sometimes or never equal to |b-a| ?