I would choose the formula D (distance to the finish line)=3-2x/2 where x is the distance run so for example for x = 1 km then 2 times 1 = 2/2=1 so D=3-1=2km which is seen to be the logical answer so it seems to corroborate the equation.
In case you can't find
(1 * 10^-6)*(7.5 * 10^18) = (1*7.5) * 10^(-6+18) = 7.5*10^12
in your head, your calculator can help.
1) D. 77%
2) C. 28.39
3) B. 13.51