Per Forums Rule that I should show my attempt at working the problem before posting my question, to my defend, I didn't know where to start actually. I just didn't know how to approach the problem & that's why I asked the question. We just started that subject yesterday in class & the homework is due this morning. As you can see, i worked out 2 problems before that, #11 & #12, but just didn't know how to approach #13. That's why I couldn't show my attempt. Just didn't know what to do with it or where to begin.

Thanks.