In chemistry, particularly solutions, you must always obey the Law of Conservation of Mass. Meaning, for solutions without reactions, the moles of solute in the solution does not change after dilution. The equation would be:
M1V1 = M2V2
(0.350 M)(225mL) = M2(175 + 225 mL)
M2 = 0.197 M
The final concentration would be 0.197 M.
