#F:" force between two charges"#

#F=k*(q_1*q_2)/r^2" Coulomb's law"#

#x:" distance between the charge of 3C and -1C"#

#x=6-0=6 #

#y:" distance between the charge of -1C and -2C"#

#y:5-0=5#

#F_1:" Force between the charge of 3C and -1C"#

#F_1=k*(3*(-1))/6^2#

#F_1=(-3*k)/36#

#F_2:" Force between the charge of -1C and -2C"#

#F_2=(k*(-1)*(-2))/5^2#

#F_2=(2*k)/25#

#F_n=(-3*k)/36+(2*k)/25#

#F_n=(-75*k+72*k)/(36*25)#

#F_n=(-cancel(3)*k)/(cancel(36)*25)#

#F_n=k/(12*25)" , "k=9*10^9#

#F_n=(cancel(9)*10^9)/(cancel(12)*25)" ; "F_n=(3*10^9)/(4*25)#

#F_n=3*10^7#