@acer 

Thanks :) I have got the first part of the question.

Will try to look at the second part now.

Thanks again for your kind help.

@acer 

this is so far what I have got.

@acer 

thanks for your reply.

and I'm trying to do the first part of the question.

when I put

soln := dsolve({des, ics}, {y(x)}, series)

it shows that

Error, (in dsolve/process_input) invalid arguments

@Carl Love 

Thanks. I have done the question :)