Thank you for the opportunity to help you with your question!
This is how you answer this question using similarity and congruence.
Given the values of height and width of the bigger circle you find the area of the bigger circle which is 1/2*12*8=48square centimetres
Using similarity and congruence we say 48/a=12/y=8/x where a is the area of the small triangle which is not given. This is how this kind of problem is solved given that the area of the small triangle i known. Please let me know if you need any clarification. I'm always happy to answer your questions.