Answer: 24 moles of
are produced.
Explanation:
To calculate the moles :

According to stoichiometry :
1 mole of
is accompanied with = 1 mole of 
Thus 24 moles of
is accompanied with =
of 
Thus 24 moles of
are produced.
The heat released by the water when it cools down by a temperature difference AT
is Q = mC,AT
where
m=432 g is the mass of the water
C, = 4.18J/gºC
is the specific heat capacity of water
AT = 71°C -18°C = 530
is the decrease of temperature of the water
Plugging the numbers into the equation, we find
Q = (4329)(4.18J/9°C)(53°C) = 9.57. 104J
and this is the amount of heat released by the water.
D=m/v. (Density equals mass over volume).
So in your case density = 4.2/6
Which equals 0.7
Your units will be grams over milliliters
So your answer is 0.7 g/ml