Solution
This one is relatively straight forward once the penny drops.
To know the temperature of the air you need to know two things, the indicated altitude on QNH and the true altitude. You know this because if it's warmer than ISA then TRUE > INDICATED and if it's colder than ISA then TRUE < INDICATED.
In the question then, whilst you have the true altitude they have not given you the indicated on QNH. They have given you a flight level which you can use to work out the indicated on QNH. So, get off the flight level 1013 and onto 1003. You now see that the INDICATED on QNH is 9730 FT. Notice that this is less than the TRUE altitude of 10,000ft. Therefore the TRUE altitude is more than the INDICATED altitude.
Looking back to the second paragraph this can only happen if the air is warmer!
Hey presto.