Acceleration, force and mass

Push three trolleys of different masses with the same forces. Which speeds up most? Then you are given readings from a trolley of unknown mass. You will make the program draw $a$ against $F$ for each trolley, and find the unknown mass from the slope of its readings.

The idea. By the second law, $a = \dfrac{F}{m}$. So a graph of $a$ against $F$ is a straight line through the origin, with slope $\dfrac{1}{m}$.

Your tasks.

1. Work out the acceleration of each trolley for every force.
2. Find the slope of the line of readings for the mystery trolley.
3. Work out the mystery trolley's mass from that slope.