Solution
Part a
For this case we can assume that each grain present a cylindrical form then the volume is given by:

For this case r= 42/2= 21ft and h = 28 ft
Then the volume for one bin is:

Part b
For this part we can do the following conversion:

And since she has 5 bins the total of bushels are:
31033.91*5= 155169.54 bushels