The quotient of a number, b, and five

What are the constants in this expression? -10.6+9/10+2/5m-2.4n+3m

15m is what percent of 60m; 3m; 30m; 1.5 km? the last one is km not m

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?