Answer
6 is the nearest tenth it did not say ten it said ten-th
Set up a proportion: 25/100 = 50/n where n = # of teens surveyed
Simplify fraction: 1/4 = 50/n
Cross multiply: n = 200
So 200 teens were surveyed.
The proportion of buses traveling more than 900 miles would be 0.0485; multiply this by the total number of buses and you will have your answer.
We find the z-score associated with 900 miles:
z = (X - μ)/σ = (900-830.11)/42.19 = 1.66
Using a z-table (http://www.z-table.com) we see that the area under the curve to the left of this, less than this, is 0.9515. This means that the area under the curve to the right of this, greater than this, would be 1-0.9515 = 0.0485.
