My equation

Step 1. Determine t*-value w/ t-table list.

T=22-1=21; t*=2.080

Step 2.Solve for x, s, and n

X=39IU/1, S=3.4 IU/1 n=22

Step 3. Margin of error

2.080(3.4IU/Sqrt(22))=+-1.51

Confidence Interval: 39+- 1.51; Range for true population mean:37.49 to 40.51

I'm curious if this is the correct formula.