Help!

1. In reaching her destination, a backpacker walks with an average velocity of 1.40 m/s, due west. This average velocity results because she hikes for 6.44 km with an average velocity of 2.53 m/s, due west, turns around, and hikes with an average velocity of 0.480 m/s, due east. How far east did she walk?

2. Two runners start one hundred meters apart and run toward each other. Each runs ten meters during the first second. During each second thereafter, each runner runs ninety percent of the distance he ran in the previous second. Thus, the velocity of each person changes from second to second. However, during any one second, the velocity remains constant. How much time passes before the runners collide?

UPDATE: I solved number 1. Can anyone help me with number 2??

Well, the answer is when the series

surpasses 50 isn't it? After that, some casework easily solves the problem.