A solution contains both iron(II) and iron(III) ions. A 50.00 mL sample of the solution is titrated with 34.80 mL of 0.02800 M KMnO4, which oxidizes all the Fe2+ to Fe3+. The permanganate ion is reduced to manganese(II) ion. Another 50.00 mL sample of the solution is treated with zinc, which reduces all the Fe3+ to Fe2+. The resulting solution is again titrated with 0.02800 M KMnO4; this time 47.80 mL is required. What are the concentrations of Fe2+ and Fe3+ in the (original) solution?

Formula for heat change:   q = mcδtwhere 
q = the heat addedm = massc = specific heatδt=  (tf - to in absolute temperature) 
note: in this case subtracting the final and initial temperature in kelvin or celsius will not make a difference)
we add everything into the formula:   δt  = t(final) - t(original)
δt  = 36.65 - 24.85δt  = 11.8° cso the change in temperature is 11.8 degrees 

q = 41.11x  4.319 x 11.8 
q= 2095.13 heat of combustion of methane.
it shows that burning 41.11g of methane gives of 2095.13 joules of energy