B or beta value is the thermal exponent of the NTC thermistor, which is defined as the ratio of the difference between the napierian logarithms of the zero power resistance at two temperatures to the difference between the reciprocals of the two temperatures.
You can calculate the RT2 using this formula:
B = 3380
T1 = 298.15 K (25°C)
RT1 = 10Kohm
T1 and T2 are expressed in K with T(K) = T(°C) + 273.15