Solve for alpha and beta, you will get them as pi/3 and pi/6 respectively.
Plug in the values of alpha and beta in the asked expression.
I'll have to ask you to post questions by writing the whole text, and not just post images of the questions.
Images are to be added only when there's a need to illustrate something.
Thus, re-post your question (and all your previous questions) by writing the text in the question box, and providing additional details (like options etc.) on the description box.