The force between two point charges is #->#
#F=1/(4pi epsilon_0) xx (Q_1*Q_2)/r^2#
where #r# is the distance between the two charges.
Here we know
#F=175 N#
#Q_1=60 muC# which is #60 xx 10^(-6) C#
#Q_2=50 muC# which is #50 xx 10^(-6) C#
#1/(4pi epsilon_0) = 9 xx 10^9 Nm^2/C^2#
So,
#175=(9 xx 10^9 xx 60 xx 10^(-6) xx 50 xx 10^(-6))/r^2#
#175=(9 xx 10^9 xx 60 xx 50)/(10^6 xx 10^6 xx r^2)#
#r^2=(9 xx 6 xx 5 )/(10 xx 175)#
#r=sqrt((270/1750)) m #
#r=sqrt(0.154285) m #
#r=0.3927 m #
#r=39.27 cm # (approx)