The force between marbles

Relevant wiki: Gravity

Well this is a really easy question, I don't understand why it is on Level 3, but ok, here it goes the answer.

$\vec{F}_{g} = G \dfrac{m_{1}m_{2}}{r^{2}}$
Since the marbles are identical we can reduce the equation to this:
$\vec{F}_{g} = \dfrac{Gm^{2}}{r^{2}}$
Just got to do some algebraic manipulations and we arrive to an expression to mass:
$m = \sqrt{\dfrac{\vec{F}_{g}r^{2}}{G}}$
After plugging in the numbers, we get the answer:
$m = 1224.071817 \text{ kg}$
Since the answers are in grams we have to convert the mass ( $m$ ) from kilograms to grams. So we proceed to multiply it by 1000 (Since 1 kg = $10^{3}$ g) and then divide it by $10^{6}$ and the answer should be close to 1 and there we go, because the answer is $\approx 1.2$ .

Obs: $G$ stands for the Gravitational Constant whose value is $6.674*10^{-11}Nm^{2}Kg^{-2}$ .