I am really stuck at these 4 questions. Pls help:

a) Two spheres of the same density have a ratio of 9 to 16 inches in surface area, If the small sphere weighs 15 kg what does the sphere weighs. Answer to the nearest 10th of KG.
b) The ratio of the volume of two cubes is 216 to 64. What is the ratio of their surface areas?
c) Determine a 90% confidence interval for µ, δ=5, x¯= 70 and n=82. Answer interval rounded to two decimal places.
d) How many people would need to be surveyed on health care to estimate the mean of an entire population to within 2 units if the std deviation was 10 and we wanted a 92% confidence level?