I find it easier to deal with these problems when I handle each statement at a time and reduce it to math.

For example, the first part states that a fish tank is half full of water. No capacity or variable is given, so give it one.

Assume the capacity of the tank is C. In this case the statement says that it is half full of water or C/2 liters is water.

The second part of the question says that after adding 10 liters the tank is 7/8 full.

This means: C/2 + 10 = 7/8 C

Now you are left with 1 equation which contains 1 variable, therefore solvable.

10 = 3/8 C
C = 80/3 or 26 2/3.

Final check is to make sure the variable you set is the one the question is asking for. In this case it is.

thank you thank you