On the original amortisation basis (from initial £400m, over 10 years), amortisation would be £40m each year.
So, after 1 year, at year ending 31 March 2013, value of rights is £360m.
If at that point change amortisation basis to do over 15 years from then, amortisation amount would be £360m/15 = £24m each year.
The revised earnings is then obtained by adding back the original amortisation for year to 31 March 2014 (+£40m) and subtracting the revised amount (-£24m) from the original earnings of £33.5m (which is EPS of 0.67 x number of shares 50m).
Worth noting that we're asked to state any additional assumptions made. I'd hope this means that we could make slightly different assumptions, resulting in different figures, and still get the marks on offer here.
Hope that helps fill in the gaps
Lynn