PLEASE HELP ASAP, I"M TO LAZY TO DO THIS 10/7=x/5

Which of the following equations could be used to solve for the value of x?

10x = 35
7x = 50
5x = 70

Given this information, which expression must represent the value of b?

What are the solutions of the system? solve by graphing. y = -x^2 -6x - 7 y = 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?