From the Cross AB/ab *Ab/ab,what Is the Recombination Frequency If

From the cross AB/ab *ab/ab,what is the recombination frequency if the progeny numbers are 72 AB/ab,68 ab/ab,17 Ab/ab,and 21 aB/ab?

A) 0.213
B) 0.271
C) 0.500
D) 0.787
E) cannot be determined