Ok so for 17:
You would use Balance=Credit-Debit.
Plug the numbers in
Balance=84-29
84-29= 55
55 would be your balance.
18:
If the freezing point was 32F then when Tim added the potassium it went DOWN 3 degrees what would it be?
Well subtract 32 and 3!
32-3=29
29 would be your answer.
19:
If the citys budget is 8,000,000 but they spend 12,000,000 that means they spend an extra 4,000,000 a year.
If i'm correct 4,000,000 would be your answer.
Hope this helped!