The aircraft needs to be at an altitude of 1,200ft and if the surface temperature was ISA (+15°) an indicated 1,200ft on QNH (1013hPa) would be fine.
Since the surface temperature is -5°C it is ISA -20°C and the aircraft will be lower than indicated.
The difference between true altitude and indicated altitude is four feet per thousand feet per degree of temperature deviation: in this example = 4 x 1.2 x 20 = 96 ft.
If the aircraft flies at an indicated 1,296ft (1,300 is fine) the true altitude will be 1,200ft.