His plasma shows a freezing point depression of 0.547 degrees
c. for an ideal solution, a 1 osm solution depresses the freezing point 1.86 degrees
c.

Given the amount of sample: 24.25 mL; 
the concentration of the titrant (NaOH) = 0.1010 mol / L NaOH
the amount of the titrant used for titration = 14.83 mL

The concentration of a solution of lactic acid is determined by:

C(lactic acid in the sample) = ((0.1010 mol / L) * (14.83mL/1000) / (24.25mL/1000)

C = 0.0618 mol