Hi Suzanna
I don't have the puzzle in front of me but if I recall correctly, the numbers next to each letter show the numbers of separate ways each letter can be coded. All the ways the vowels can be coded are given in the grid opposite so there are 6'e's for example.
I managed to work out my first two consonants 'p' and 'k' I think, by logical inference and the rest by a mix of logic and good old-fashioned trial and error.
It was a slog but if you have the time next week too, stick with it, the end game is worth the effort.
And, just a tip, keep your trials and 'calculations' well separate from the grid itself, I made numerous 'redrafts', the only saving grace was that it wasn't completely the 'back to the drawing board' experience you often get with numericals!