The rule that we will use to solve this problem is:
M2*V1 = M2*V2 where:
M1 is the initial concentration = 3.5 m
V1 is the initial volume = 0.25 l = 250 ml
M2 is the final concentration = 9 m
V2 is the final volume that we need to find
Substitute with the givens in the above equation to get V2 as follows:
3.5*250 = 9*V2
V2 = 97.2223 ml
