The temperature of a brass cylinder of mass 100g was raised to 100 degree Celsius and transferred to a thin aluminum can of negligible heat...

The amount of heat lost by brass cylinder is transferred to paraffin. The amount of heat loss by the brass cylinder is given as

= mass x heat capacity x change in temperature

= 100 x 380 x (100 - 20) joules

The amount of heat gained by paraffin is given as

= mass x heat capacity x change in temperature

= 150 x heat capacity x (20 - 11)

Since amount of heat is constant, 

100 x 380 x (100 - 20) = 150 x heat capacity x (20 - 11)

Solving this, we get the heat capacity of paraffin as 2251.8 J/kg/K. 

In this solution, heat loss to aluminum is neglected since heat capacity of the aluminum can is negligible. Any other heat loss has also been neglected.

Hope this helps.