Answer:
7km
Step-by-step explanation:
[tex] \frac{1}{3} x + \frac{1}{4} x = \frac{4}{12} x + \frac{3}{12} x = \frac{7}{12} x \\ \\ \\ x - \frac{7}{12} x = \frac{12}{12} x - \frac{7}{12} x = \frac{5}{12} x \\ \\ \frac{5}{12} x = 5 - - - > x = 12[/tex]
[tex]12 \times \frac{7}{12} = 7[/tex]