Let's apply the principle of conservation of energy.
Heat of metal = Heat of water
mCmetalΔT = mCwaterΔT
Applying the given values,
(45 g)(Cmetal)(100 - 28 °C) = (130 g)(4.18 J/g-°C)(28 - 25 °C)
Solving for Cmetal,
Cmetal = 0.503 J/g°C
Therefore, the heat capacity of the unknown metal is 0.503 J/g°C.