Given information:

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

We need to calculate the total number of notebooks: $P + Q + X + Y + Z$.

1. Using equations (ii) and (iii): $P = 13$ Then, $Q = P - 5 = 8$.

2. With $P = 13$ and using equation (v): $X = P - 5 = 8$

3. Using $X = 8$ in equation (i): $Z = X + 8 = 16$

4. Finally, using $X = 8$ in equation (iv): $Y = 28 - 8 = 20$

Total Calculation: $P + Q + X + Y + Z = 13 + 8 + 8 + 20 + 16 = 65$

The cost of all the notebooks is:

$65 \times 40 = Rs. 2600$