If a high-speed industrial drill with the diameter of 42 in and a torque of 15 lb-ft develops a power of 2.8 hp. a) what is the speed of the drill in RPM? b) what is the force?

I won't solve it for you, but I'll show you how to do it:

a) Power = torque times rotational speed. You know the power and torque, so solve for rotational speed. You'll have to use the conversion factor 1 HP = 550 ft-lb/s.

b) Torque = force times radius. Solve for force.

Help me solve this problem, I am totally lost
-5c+9c =-20

-5c+9c=-20

To get started, do you know what -5+9 equals? Hence, what does -5c+9c equal?

Um think about it this way.

First thing is to look at the terms 5c and 9c. Those equate to (c+c+c+c+c) and (c+c+c+c+c+c+c+c+c). The 5 and the 9 are the number of c you have. So you can add the numbers in front of the variable. Then you have a number of c that will equal -20. So if you divide each side by the number you c you have after you've added the two numbers together you will get your answer.