Kristen can run at 9kmh-1 and walk at 3kmh-1. She completed a 42km marathon in 6 hours. What distance did Kristen run during the marathon?

Kristen completed 42 km. We will imagine that she ran all 6 hours. = > 9 * 6 = 54 km which is more than she actually completed. So we will find a 9 Multiple less than 42 km and that will be 36 km. (9 * 4 = 36 km completed by running) and the rest until 42 were completed by walking (3 * 2 = 6; 6 + 36 = 42).