college physics
posted by cat .
An aluminum cup contains 225 g of water and a 40g copper stirrer, all at 27°C. A 400g sample of silver at an initial temperature of 87°C is placed in the water. The stirrer is used to stir the mixture gently until it reaches its final equilibrium temperature of 32°C. Calculate the mass of the aluminum cup. answer in g
my equation looked like this:
(1/900)[400 g x 225 g x (8732/3227)  (40 g x 387 g)  225]
I honestly don't think my numbers are right. My answer was 85 g, and the homework says that I am within 10% of the correct answer though...help please!

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