I was wondering I any of you could help me with these two problems.

1.

A contractor estimated that one of his two bricklayers would take 9 hours to build a certain wall and the other 10 hours. When the two bricklayers worked together, however, 10 fewer bricks got laid per hour. With both men working on the job it took exactly 5 hours to build the wall. How many bricks did it contain?

I think this one doesn't have an answer. It's impossible to calculate.

2.

You have a can with four balls of different colors. Randomly you draw two at a time, then paint the first ball to match the second. What is the expected number of drawings before all balls are the same color?

This one...I don't know