How much coal must be burned in order to heat 7 tons of water taken at a temperature of 25 degrees

How much coal must be burned in order to heat 7 tons of water taken at a temperature of 25 degrees to 100 degrees and turn 0.5 tons into steam?

Given: m1 (water mass) = 7t = 700 kg
t1 = 25 C
t2 = 100 C
c (specific heat of water) = 4200J / (kg × C)
m2 (steam mass) = 0.5t = 500kg
L (specific heat of vaporization of water) = 2.3 × 10 ^ 6 J / kg
q (specific heat of combustion of coal) = 2.7 × 10 ^ 7J / kg
Find: m3 (mass of coal)
Decision:
Heat (Q1) – spent on heating and evaporating water is equal to heat (Q2) – released during the combustion of coal, i.e. Q1 = Q2
Q1 = cm1 (t2-t1) + Lm2
Q2 = qm3
Therefore cm1 (t2-t1) + Lm2 = qm3
Hence m3 = (cm1 (t2-t1) + Lm2) / q =
= (4200 × 7000 × 75 + 2.3 × 10 ^ 6) / (2.7 × 10 ^ 6) = 124.5kg