Hello Nicole. I am happy to help.
We know that molarity is the moles of solute per liters of solution. In your problem you would like to know the new molarity after diluting with water.
The amount of solute in the concentrated solution is equal to the amount of solute in the diluted solution.
So we can say M1V1=M2V2
So here is what you know:
Initial : M1= 1.25 V1=35 mL
Final : M2= ? V2= 55mL
Now you can plug into the equation M1V1=M2V2
Rearrange for M2. gives:
M2= M1 X (V1/V2)
M2 = 1.25 (35mL/55mL)
Please let me know if you have any questions. I am also available if you would like further review in a tutor session.