How will you formulate the appropriate null and alternativehypotheses on a population mean.

Null Hypothesis - It states that there no relationship/difference between sample means or proportions. It is represented by $H_0$. It takes "=", "$\le$" or "$\ge$" operators depending on the wording of the hypotheses test.
Alternative Hypothesis is a claim about the population that is contradictory to $H_0$. It is represented by $H_1$. It takes "$\ne$", "<" or ">" operators depending on the wording of the hypotheses test.
$$\begin{gathered} \text{Null hypothesis }{H}_0÷\mu =40 \\ \text{Alternative Hypothesis }{H}_1÷\mu \ne 40 \end{gathered}$$
Here, we test whether the mean of a population is statistically different from a known or hypothesized value (40).
This is a two tailed test, since the alternative hypothesis contains "$\ne$" symbol.
A right tailed test contains a greater than (>) symbol in the alternative hypothesis.
If we are asked to test if the population mean is greater than 40, we use a right tailed test.
Then, the null hypothesis states that the mean is less than or equal to 40. The alternative hypothesis would be that the mean is greater than 40.
A left tailed test contains a less than (<) symbol in the alternative hypothesis.
If we are asked to test if the population mean is less than 40, we use a left tailed test.
Then, the null hypothesis states that the mean is greater than or equal to 40. The alternative hypothesis would be that the mean is less than 40.