For the significant figures question, your answer can only have three significant figures in it because the time specified contains only three sig-figs. Your answer can only have as many sig-figs as your least precise value, which is the time. Also, your time only goes out to one decimal place, so your answer can only go out to one decimal place. If your answer winds up being something like 0.15694, then the answer you would have to provide is 0.2. While the answer doesn't have three sig-figs in it, it's limited to only one place after the decimal which has precedence. This is why scientific notation is used. It helps get rid of the decimal place problem. For 0.15694, you could write that in as 15.7x10-2 and it would be just fine.