Hello fellow statisticians!
it's been awhile since I've done stats and everything has completely escaped me. I'm trying to conduct hypothesis testing for the question below. Everyone has been using the Chi-squared test and I feel that they are wrong. I think it should be a poisson distribution but the change in the control is throwing me off. Any help would be greatly appreciated! Thanks a million! Here's the question:

Suppose there has been the introduction of treatment to reduce the number of accidents at the Nathan road-waterloo road junction (treated site). Also suppose the junction of mongkok road and Shanghai street has been chosen as the control site. After in months, the accident frequencies of these two junctions have been tabulated below

Before After
Nathan 30 18
Mong Kok 15 12

Use an appropriate statistical test to test whether the treatment has been effective.

I'm assuming the change in Mong kok is just a natural change as it hasn't been treated.... so we're just weighing the treated site against the natural change

I did an initial hypothesis of

Thanks in advance for any help. :D