Does this worksheet make sense?

Hello

This is my first post to the forum so... Hello!!

I am looking to change car in the VERY near future and I wanted to know if i'd see any real benefit from changing to diesel by using MPG best scenarios.
It's been a while since I've used any sort of formulas as simple as they may be but i think I've cracked it.. Would someone be able to look it over and tell me that it all makes sense and it's all true for what i need?

Can anyone suggest anything that I could add to it to help me out some more?

Any help and additions are most welcome

Thanks.