Find the order of magnitude of the number of stars in the milky way

the "diameter" (in "number of stars wide") 10^21 / (4*10^16) = 2.5 * 10^4 "stars" area of disc = pi r^2 = 3.14 * (1.25 * 10^4) ^2 = aprx 4.3 * 10^8 star-sq (in "number of stars-squared") height = 10^19 / 4*10^16 = 2.5*10^2 stars high volume = A*h = (4.3 * 10^8) * (2.5*10^2) = 10^11 stars