How to calculate the population mean? Is 100/100 correct? Or use Poisson distribution?

This question has 2 parts. A company produce printed circuit boards (PCBs). A random sample of 100 PCBs has been taken from a recent production run and the number of defects on each board recorded. The data are provided below: Number of defects Observed frequency 0 22 36 2 21 12 4+ 9 The company would like to carry out a x2-square goodness of fit test, with the hypotheses Ho : The data are from a Poisson distribution; Ha : The data are not from a Poisson distribution. i) What estimate for the population mean defects per board should be used in this test? O 1.0 12.0 O 0.6 60