Coffee virtual Lab

Question

I got the question from this virtual lab http://chemcollective.org/activities/autograded/115 but I dont understand how to get the answer.

 An eccentric chemistry professor (not mentioning any names) stops in every day and orders 200ml of Sumatran coffee at precisely 65.0°C. You then need to add enough milk at 5.00°C to drop the temperature of the coffee, initially at 95.0°C, to the ordered temperature.

Calculate the amount of milk (in ml) you must add to reach this temperature. Show all your work in the provided spaces.

In order to simplify the calculations, you will start by assuming that milk and coffee have the specific heat and density as if water. In the following parts, you will remove these simplifications. Solve now this problem assuming the density is 1.000 g/ml for milk and coffee and their specific heat capacity is 4.184 J/(g ºC).

Answer 1

Heat lost by coffee = heat gained by milk

heat lost by coffee = q = mC∆T = (200 g)(4.184 J/g/º)(30º) = 25,104 J

heat gained by milk = q = mC∆T = (x g)(4.184 J/g/º)(60º)

25,104 J = (x g)(4.184 J/g/º)(60º)

x g = 100

100 g milk = 100 ml milk