Well the width is 0.20 meters. Since there are a hundred centimeters in a meter, we just have to move the decimal point two times to the right to get a 20 centimeter width.
I'm not sure how many sign fig's you are required to have.
However I think the final answer would be 0.05 Moles, because of the .5g, that is considered 1 sign fig.
The correct answer is C. Litmus Indicator