A3.50 kg block of lead at 14.4°c comes in contact with a block of copper at 88.4°c.

1.48 kg

Explanation:

The conservation of energy states that energy cannot be created or destroyed but can be converted from one form to another. Hence, in this case, energy lost by the copper should equal to the energy gained by the lead. Hence,

Energy Lost by Copper = Energy Gained by Lead

mcT = mcT (Bolded is for copper, italicised is for lead)

m(387)(88.4 - 55.9) = (3.50)(128)(55.9 - 14.4)

12577.5m = 18592

             m = 1.48 kg (3 sf)

(Note: Thermal energy can be calculated using Q = mcT where m is the mass, c is the specific heat capacity and T is the change in temperature)