How much kerosene can be heated from 30 to 40 degrees, if a fourth of the energy obtained from the combustion

How much kerosene can be heated from 30 to 40 degrees, if a fourth of the energy obtained from the combustion of 20 kg of coal was used to heat it?

The formula for calculating the heat required for heating:
Q1 = cm1T;
The formula for calculating the heat released during combustion:
Q2 = qm2;
Since 1/4 of the heat of combustion is used for heating, then:
Q1 = 1 / 4Q2;
cm1T = 1/4 qm2;
We express the necessary mass of kerosene m1:
m1 = (qm2) / (4cT);
q and c are tabular values:
q = 30 * 10 ^ 6 J / kg
c = 2100 J / (kg * C)
Temperature difference T = 40-30 = 10
Substitute the values:
m1 = (30 * 10 ^ 6 * 20) / (4 * 2100 * 10) = 7142.8kg
Answer: 7142.8kg