On 5a, I am unsure where to find the information on how to calculate which will strike the shore first, the short or long wave length?
There is a description on p. 254 in the book of what happens to a mixture of short and long waves as they travel away from their source area. You do not need to make any calculations, but if you did, you could answer the question using the formulas given on the same page relating wave celerity & group velocity to wavelength.