Step 1 :The null hypothesis is a general statement or default position that there is no relationship between two measured phenomena, or no association among groups. In this case, the null hypothesis would be that the proportion of trees that the beetle infests is 12%, as it is generally known.
Step 2 :The alternative hypothesis is what you might believe if the null hypothesis is concluded to be untrue. The alternative hypothesis is the opposite of the null hypothesis. Since Peter wants to test if more than 12% of trees have been infested, the alternative hypothesis would be that the proportion of trees that the beetle infests is more than 12%.
Step 3 :Therefore, the correct answer is b.) Null hypothesis: $p=0.12$, Alternative hypothesis: $p>0.12$.
Step 4 :Final Answer: \boxed{\text{b.) Null hypothesis: } p=0.12, \text{Alternative hypothesis: } p>0.12}.