The Specific Heat formula is:
c = ΔQ / (m × ΔT)
Where:
c: Specific Heat , in J/(kg.K)
ΔQ: Heat required for the temperature change, in J
ΔT: Temperature change, in K
m: Mass of the object, in kg
So substitute the numbers in; Calories should be converted into joules
c = 1560(4.184)/(312*15)
c = 1394.666