Speed is calculated as the ratio between the distance travelled and the time it takes to travel the distance,

$$
begin{align}
v = frac{d}{t}
end{align}
$$

We rearrange Equation 1 such that the distance $d$ is isolated on one side of the equation.

$$
begin{align*}
d = vt
end{align*}
$$

We convert the time in seconds using the conversion $1;text{min} = 60;text{s}$. Using $v = c$ for the speed, the distance of Mars from Earth is

$$
begin{align*}
d &= ct \ &= left(3.0times 10^{8};frac{text{m}}{text{s}}right)(12;text{min}) left(frac{60;text{s}}{1;text{min}}right) \ &= boxed{2.2times 10^{11};text{m}}
end{align*}
$$

$d = 2.16times 10^{11}$ m