How much kerosene burns in 1 minute in a stove with an efficiency of 40%, if 2 liters

How much kerosene burns in 1 minute in a stove with an efficiency of 40%, if 2 liters of water are heated on it from 15 to 100 degrees in 10 minutes?

Given:
k = 40%,
V = 2l,
ρ = 1000kg / m ^ 3 – water density,
t1 = 15 ° С,
t2 = 100 ° С,
t = 10min,
c = 4200J / (kg * deg) specific heat capacity of water,
q = 4.6 * 10 ^ 7 – specific heat of combustion of kerosene;
Find: m / t, where m is the mass of burned kerosene.
During the combustion of kerosene of mass m, the amount of heat is released Q1 = m * q;
Of this amount, only k * Q1 part is spent on heating water.
To heat water, you need the amount of heat
Q2 = M * c * (t2 – t1),
where
M = ρ * V = 1000kg / m ^ 3 * 2 * 10 ^ (- 3) m ^ 3 = 2kg is the mass of water;
From the heat balance equation:
Q2 = k * Q1;
k * m * q = M * c * (t2 – t1);
m = 2 * 4200 * 85 / [4.6 * 10 ^ 7 * (40% / 100%)] = 0.039kg = 39g.
Kerosene consumption for 1 min: m / t = 39g / 10min = 3.9g / min.