#F_c=7*k " you can write " 9.10^9 " instead of k"#
Explanation:
#"force between two charges is given by :"F_c=(k*q_1*q_2)/d^2# #F_c=(k(-105)*(-15))/15^2# #F_c=(k*105*cancel(15))/cancel(15)^2# #F_c=(k*105)/15# #F_c=7*k " you can write " 9.10^9 " instead of k"#