Two charges valued 1 c and 2 c are sitting 200 centimeters apart from one another find the force exerted on the charges by one another

My friend had this for homework and he allowed me to put his answer here.

His answer: F=kq1q2/42 = 4.2 x10-2 N If r - > (1/8) r, r2 - > (1/64) 42 and so, F = 64 (4.2 x 10-2 N) = 1.69 N

In short, the answer is: 1.69 N