Hi Mark,
Let's work the first one and I'll leave you to do the rest (or post again if you get stuck)
From Exercise N6 on p 3.1.21:
14gph for 88 min and we want the fuel required at startup in gallons and litres plus we want flight fuel in gallons and litres. The operator specifies a fixed reserve of 10 gallons, taxi/startup allowance of 2 gallons and no variable reserve.
First off, let's find how much fuel we need for the 88 minutes of flight (the flight fuel). You can use a calculator for this step but we'll do it with the CR3 for now. On the CR3, line up the burn rate of 14 gph on the outer scale against the "1:00" or 1 hour marker of the inner scale. The CR3 is now set up to read fuel over time with fuel amounts on the outside scale and time on the inside scale calibrated for a fuel burn rate of 14 units per hour (gallons in this case).
We want the time of 88 minutes so find "88" on the inner scale and read off the fuel burn from the outside scale. You'll see it comes to 20.5 gallons.
To calculate the other values we use a calculator. I'll create a simulated fuel plan with columns for gallons and litres so you can better see how the values all fit together. I have used the supplied constants of 1 gallon = 3.78 litres.
FUEL
 ....................  GALLONS
 LITRES

Flight Fuel:  88 min @ 14 gph  20.5 gallons  20.5 x 3.78 = 77.49 round up to 78 litres 
Variable Reserve:  ....................  None  None 
Fixed Reserve:  ....................  10 gallons  10 x 3.78 = 37.8 litres 
Taxi/Startup  ....................  2 gallons  2 x 3.78 = approx 7.5 litres 
FUEL AT STARTUP  ....................  20.5 + 10 + 2 = 32.5 gallons  78 + 37.8 + 7.5 = 123.3 litres round to 123 litres 
Fuel at startup is the flight fuel plus all reserves and allowances together so we simply add the flight fuel plus the fixed reserve plus the allowances to get the final total.
Have a go at the others in N6 now and let me know if you get stuck or have any more problems.
Cheers,
Rich