Final answer:
The mass of the last screw Cayden adds is 3.855 g.
Step-by-step explanation:
To find the mass of the last screw, we need to subtract the mass of the screws on the scale without the last screw from the mass of the scale with the last screw. The difference in mass will give us the mass of the last screw. Here's how:
Mass of screws on the scale without the last screw: 80.955 g
Mass of the scale with the last screw: 84.81 g
Mass of the last screw = Mass of the scale with the last screw - Mass of screws on the scale without the last screw = 84.81 g - 80.955 g = 3.855 g
Therefore, the mass of the last screw Cayden adds is 3.855 g.