How would you synthesize compound b from compound a and any other reagent needed?

Explanation:

With no information about the structures of A and B is imposible to tell exactly how would you synthesize one from the other.

Synthesize process may involve one or many reactions to achive the desired product.

To determine what type of reaction you need to perform, is important to compare A with B, and see the differences: what atoms or functional groups are in one of that that aren't in the other.  

Once done that, you can start to describe the reactions (steps) you need to do.

Some types of reactions are (see the figure):