A research study examined the cholesterol levels in two groups, intervention versus placebo, to see whether consuming more salmon in the diet would make a difference on cholesterol levels. The mean cholesterol level of the 60 people in the placebo group was 240 with a SD of 20. The 60 people in the salmon consumption group had a mean cholesterol level of 210 with a SD of 21. Calculate the z, t, or chi-square test and choose the value in the answer below.

Select one:

 a. 6.91

 b. 7.23

 c. 8.01

 d. 5.38

Please show your work. Thank you