As per the information provided in the question:

Statement 1 -> Z = X + 8 ….(i)
Statement 2 -> P + Q = 21 ….(ii)
Statement 3 -> Q = P – 5 ….(iii)
Statement 4 -> X + Y = 28 ….(iv)
Statement 5 -> P = X + 5 ….(v)

Total number of Books = P + Q + X + Y + Z

Solving equations (ii) and (iii), we get:

P = 13
Q = P – 5 = 8

Using above result and equation (v), we get: X = P – 5 = 8
Using above result and equation (i), we get: Z = X + 8 = 16
Using (iv), we get: Y = 28 – 8 = 20

So, P + Q + X + Y + Z = 13 + 8 + 8 + 20 + 16 = 65
So, total cost of all the notebooks = 65 × 40 = Rs. 2600