Problem 1.2 10 yrs - Estimate the total surface area these grains wold cover if you could put them side by side. You can assume that the grains are approximately spherical so each grain covers an arearz, where r is the grain's radius. State your answer in square light -years . Problem 1.3 10 pts - Estimate the total surface area the cloud covers , assuming that its matter density is like that of a typical molecular cloud , about 10'21 glcm 3. (Him : First calclate the cloud's volume from its mass and density. Then determine the cloud radius using the formula for the radius of sphere ,R : (3 X volume/4)l/3.] State your answer in square light -yea.rs . Problem 1.4 5 pm - Based on your answers to Problems 1.2 and 1.3, what do you think the chances are that a photon passing through the cloud will hit a dust grain 7