Physics
posted by Jenn .
Four penguins are being pulled along very slippery (frictionless) ice by a curator. The masses of the three penguins are given below and so are two of the tensions. Find the penguin mass that is not given.
12kgUnknown111N15kg20kg222N
After drawing the freebody force diagrams, I was lost.

Write the equations
F=ma
222=(20 + 15 + 12 + M)a
111= (12+M)a
so solve it, two unknowns, two equations. However, it is not that hard. There is another equation.
222111 =(15+20)a so solve for A here, then solve for M from above. 
1. Which of the following is not an example of an energy transfer?
1. A roller coaster being pulled to the top of the first hill
2. A roller coaster standing still allowing people to get on
3. A roller coaster falling down a hill
4. A roller coaster coming to a stop at the end of ride 
thank you so much! I think I just overcomplicated the problem. thank you for making it much easier!