I need help plz and explination its confusing

12.56

Step-by-step explanation:

The formula for circumference is either πr² πd. Thats basically just multiplying. All you have to do is take the the diameter and multiply it times pi and you get the answer. In some cases they want you to use the radius; radius is diameter divided by 2. Example is if 4 is the diameter 2 is the radius. For this one i did 4 times 3.14(pi).

I hope that helps!

reduce the friction between its moving parts

step-by-step explanation:

in fact, by reducing the friction between the moving parts of the machine, it is possible to reduce the energy wasted due to this friction; therefore, more input energy is converted into useful work, and this will improve the efficiency of the machine.