Kristen can run 9km/h and walk 3km/h. she completed a 42km marathon in 6 hours. what distance did kristen run during the marathon?

Let

x = distance traveled running.

y = distance traveled walking.

x + y = 42

1 / 9x + 1 / 3y = 6

Solving the system of equations:

-3 * (1 / 9x + 1 / 3y) = - 3 * (6)

-1 / 3x + - y = - 18

Then,

x + y = 42

-1 / 3x + - y = - 18

Adding up:

-1 / 3x + x = 24

2 / 3x = 24

x = (3/2) * 24

x = 36 Km

Answer:

kristen ran 36 Km during the marathon