Hi A320',
As 1019 is higher than 1013, we shall need to add 27' * 6hPa = 162' onto 13,500 to give us our altitude above sea level. This gives us 13,662' above sea level.
However the question states that our "true" altitude is 13,500'.
As the true altitude is less than our altitude above sea level (true altitude of 13,500 as opposed to 13,662), the temperature must be colder than ISA.
Remember, if the column of air below you is colder than ISA then you are lower than the altitude above sea level. If the air is warmer than ISA then your true altitude will be higher than that indicated.
Best wishes,
Charlie Zulu.