If you look at the standard cost card, the total input of materials comes to 1.2 litres, but the expected output is 1 litre.
Therefore if they input 5,750 litres they would expect to produce 1/1.2 x 5,750 litres
Q49.6 (I think you mean 49.8 if you are using the current edition 🙂 )
In total they actually used 7,500 kg. The question says that the standard mix is 10% for P, 20% for Q, etc. So out of the 7,500 total, 10% (i.e. 750) should be P; 20% (i.e. 1,500) should be Q, and so on.