Värmeuppgift, upphettning och nedkylning

Hej, jag fattar verkligen inte hur man löser denna uppgiften. Har det med Newtons lag om nedkylning eller är jag helt borta?

In lab you submerge 100 g of 40°C iron nails in 100 g of 20°C water (the specific heat of iron is 0.11 cal/g?°C.)

(a) Equate the heat gained by the water to the heat lost by the nails, and show that the final temperature of the water becomes 22°C.

(b) Your lab partner is surprised by the result and says that since the masses of iron and water are equal, the final water temperature should be closer to 30°C, halfway between. What is your explanation?