This question is asking for 15% of £7.99
If you can do it using a calculator, just do this:
15÷100 × 7.99
And that would give you the discount which would be £1.20
If you can't do it using a calculator, you would need to break the percentage of 15% into 10% and 5% and work these out seperately:
10% of £7.99 = 0.799 = 80p
5% of £7.99 (half of above answer) = 0.3995 = 40p
= £1.20
So, to conclude, the amount of discount would be £1.20
(So the notebooks would now cost £6.79)