The amount of heat needed to increase the temperature of a substance by [tex]\Delta T[/tex] is given by
[tex]Q=mC_s \Delta T[/tex]
where
m is the mass of the substance
[tex]C_s[/tex] the specific heat capacity
[tex]\Delta T[/tex] the increase in temperature
In our problem, the mass of the water is m=750 g, the specific heat is [tex]C_s = 4.2 J/g ^{\circ}C[/tex] and the amount of heat supplied is [tex]Q=31500 J[/tex], so if we re-arrange the previous formula we find the increase in temperature of the water:
[tex]\Delta T= \frac{Q}{m C_s}= \frac{31500 J}{(750 g)(4.20 J/g^{\circ} C)}=10^{\circ}C [/tex]
