Question 43600
The time spent to travel x km with the car is {{{x/30}}} hours. The time spent to travel x km on foot is {{{x/10}}} hours. We want to know at what x this equation is true:

{{{x/30 + x/10 = 2}}}
{{{x/30 + 3x/30 = 60/30}}}
{{{x/cross(30) + 3x/cross(30) = 60/cross(30)}}}
{{{4x = 60}}}
{{{x = 15}}}

Therefore, they were 15 km from home when the car broke.