Okay, here we have this:
Considering the provided information, we are going to calculate the requested value, so we obtain the following rule of three:

Solving for x:

Finally we obtain that 87.5mL of water should be used for 250g of plaster.
The answer is B because if you add the to angles together you create a straight line.
If you look at the end points you see they are different the hole one means the line doesn't reach that point but gets really really close the solid one means starting at that point.