If each you have 9900g of donuts and each donut has a mass of 150g, we can divide 9900 by 150 to figure out how many donuts we have. To do this, we first have to figure out how many times 150 goes into 990. It goes into 6 times and has a remainder of 90. Now we have to figure out how many times 150 goes into 900. It goes in 6 times, meaning that our answer is 66 donuts.
C. This is because the water has undergone a physical change meaning that the effects can be reversed. If nothing was added or lost from the water the ice would be the exact same weight.