How to calculate the observed and expected for a chi squared?

Hello in a scenario like the following how do I calculate the observed and expected values to put into a chi squared test?





A drug against cancer is being tested. The drug and a placebo is being tested and the following results obtained.





Drug A - Improvement = 146 No effect = 30


Placebo - Improvement = 23 No effect = 153





Is there a statistical difference between the groups?





Im sure there is a quick way of starting it. like adding them up and multiplying them by something but I cant remember it!





Help - I have an exam tomorrow!How to calculate the observed and expected for a chi squared?
see the Pearson's chi square test