Random Samples of 4 Items Are Selected from a Manufacturing $\Sigma$

Random samples of 4 items are selected from a manufacturing process at regular intervals and a certain quality characteristic is measured. After 25 samples, $\Sigma$ X = 15,350 and $\Sigma$ R = 411.4
What is the sample size?

A) 4
B) 25
C) 100
D) 20