Answer:
3.855 gm.
Explanation:
We have been given that Cayden has several screws on a scale and the scale reads 80.955 g. Cayden added 1 more screw, the scale reads 84.81 g.
To find the mass of last screw we will subtract mass of screws before adding the last screw from mass of all the screws after adding last screw.

Therefore, the mass of the last screw is 3.855 gm.