Hello IntrusionThanks for showing us your working.

The diagram shows the forces acting on the book.

Resolve at right angles to the plane:

So your first equation is correct.

And you have correctly calculated the acceleration (although you have rounded off a bit too much; the answer is more accurately 63.33.)

But when you resolve down the plane:

So your 'friction force' equation is wrong. You need to take the component of the weight into account.

Can you complete it now?

Grandad