Statistics Hypothesis Testing finding out test stat and critical value 
For a) 
$$z =\frac{ \bar{x} - \mu }{ \frac{\sigma }{ \sqrt n}}$$
I have deciphered that sample mean is $$\frac{20 + 23 + 21 + 22}{ 4} = 21.5$$
I came up with $1.29099..$ for Standard Deviation.
Sample size is $4$ since $4$ sharks
$$z =\frac{ 21.5 - 20 }{ \frac{1.209 }{ \sqrt 4}}$$
I came up with $2.168870...$ for the test statistic.
For critical value of $z$, I used the given alpha to find the value of $2.326$ from a confidence interval of 98%.
What are the answers and what am I doing wrong ?
(Thank you for the edit)

Your test statistic should be $2.3238$. I don't know how you got the value you got. You should calculate $(21.5-20)/(1.291/\sqrt{4}) = 2.32378...$
The critical value should be $4.54$. The question suggests doing a one-tailed test (because the biologist thinks that the sharks will be longer than $20$.) There are $4-1=3$ degrees of freedom. 
(For a two-tailed test, the critical value would be $5.841$.)
