Question

Can you help me on this problem please

Answer 1

First all numbers must be presented in the same format. So change the fractions to whole numbers.

5/8 = .633

6 5/8 = 6.633

Now you can start.
Add all the negative numbers first.

I add

(-) .633
0.4
0.4
6.0
2.9
3.2
-------------
-13.533 centimeters

Add the positive numbers together
3.2
6.633
0.3
---------
10.133

Now you can subtract

-13.533
Minus
10.133
--------
-3.4 centimeters
So the water level is down by -3.4 centimeters over the entire 9 months period.