Part (a):

KINDOFBUS(Manufacturer, Model, MaintIntervalMiles, MaintIntervalDays,
                        OilGrade, OilCapacity)

BUS(LicensePlate, Manufacturer, Model, DateAcquired,
         DateManufactured, MilesWhenAcquired)
    (Manufacturer, Model) foreign key to KINDOFBUS

MAINTENANCE(LicensePlate, Mileage, MaintenanceDateAndTime, Description)
    LicensePlate foreign key to BUS

DRIVER(DriversLicense, FirstName, LastName, MiddleNameOrIinitial,
                BirthDate, CellPhone, Phone, LastTrainingDate)

DISPATCH(LicensePlate, DispatchTime, ReturnTime,
                     DispatchMiles, ReturnMiles, DriversLicense, Comments)
    LicensePlate foreign key to BUS
    DriversLicense foreign key to DRIVER

Note that there are other primary key combinations possible for MAINTENANCE and DISPATCH, or you could always just make up a synthetic key.  You could also use a synthetic key for KINDOFBUS.  Take note of the way we annotate a composite foreign key "(Manufacturer, Model) foreign key to KINDOFBUS".

Part (b):

So, each record in the dispatch tables uses 302 bytes.  We then calculate

Part (c):

Instead of the single table DISPATCH from part (a), we have

DISPATCH(LicensePlate, DispatchTime, ReturnTime,
                     DispatchMiles, ReturnMiles, DriversLicense)
    LicensePlate foreign key to BUS
    DriversLicense foreign key to DRIVER

COMMENT(LicensePlate, DispatchTime, Comments)
    (LicensePlate, DispatchTime) foreign key to DISPATCH

Again, you could use various alternative primary key combinations, or a synthetic key. 

The size of each record in the DISPATCH table now shrinks 255 bytes, because the Comments field is gone.  So each record takes 302 – 255 = 47 bytes.  So the space for DISPATCH is now

The number of bytes per record in COMMENT is

and the COMMENT table has about 5% ´ 396,000 = 19,800 records.  Thus the space for COMMENT is

So the total space taken is 17.8 + 5.1 = 22.9 MB.  The space saved is 114.1 – 22.9 = 91.2 MB.