A $4\mathrm{.}0$ nC charge is placed $2\mathrm{.}0$ cm from a fixed $-1\mathrm{.}0$ nC charge. If the $4\mathrm{.}0$ nC charge is moved to a point $6$ cm from the $-1\mathrm{.}0$ nC charge, by what factor does the magnitude of the force on the $4\mathrm{.}0$ nC charge change?