You can figure this out using the equation for specific heat: q=mcΔT; where q is the heat, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature (in °C or K).
In this case we're solving for q, given m = 20000 g, c = 4.18 j/g°C, and ΔT = 35°-0°=35°. This means q = 20000 x 4.18 x 35 = 2 926 000 J, or 2926 kJ.
