Following the rule of thumb in dilution, the equation that can be used to solve this problem is:
C1V1 = C2V2
where:
C1 = concentration of solution 1
V1 = volume of solution 1
C2 = concentration of solution 2
V2 = volume of solution 2
(0.1)(V1) = (0.05)(750)
V1 = 375 mL
This shows that 375 mL of a 0.1 m NaHCO3 solution is needed in order to dilute it to a 0.05 m NaHCO3 solution of 750 mL.