Hello,
The correct answer is D. You need to start this problem by writing an equation.
It should be: 10k + 50 > 300 because she is getting $10 per kilometer and she already has $50 to add to her total. Her goal is to have more than $300.
Next solve the equation,
10k + 50 > 300
10k > 250
k > 25
That is how we get choice D.
Good luck,
MrEQ