Reading and Use of English
Part 4: Key word transformations
How to act?
Step 3: fill in the missing words. Remember! You have to use 2 - 5 words. Less or more will cost you points. Collocations like 'don't' or 'I'm' will count as two words. You have to use the word 'idea'.
What does it mean when you are 'in favour of something'? It means that you would prefer to do something, or that you think it is a good idea to do something.
Use that to form your sentence:
Joan thought it would be a good idea to go to the museum.