Are you supposed to be on only one side or write both the pros and the cons?
I find 150 words to be REALLY short. It's always harder for me to write less than to write more.
But what you do is jot down two or three points you want to make, build a coupld sentences around each one, and then come up with a decent opening and conclusion. Try it. Post it. Let us see.
P.S. - welcome to the forums!