Final answer:
If a firer can shoot a 30mm group at 100m, then theoretically, the group size would increase proportionally with distance to 90mm at 300m, assuming a simple linear relationship and disregarding other factors.
Step-by-step explanation:
The student's question refers to the effect of distance on the accuracy of firing a projectile, in this case, a bullet from an M4 with iron sights. According to the theory of the group, if a firer is capable of shooting a 30mm group at 100m, then at 300m, we would expect the group size to theoretically increase proportionally to the distance, assuming a linear relationship and ignoring other factors such as wind, air resistance, and gravity. Therefore, if the group size is 30mm at 100m, at 300m, the group size would be approximately 90mm, as it is triple the distance.