Hi!
First, find the total percent of vehicles with at least 3 people.
15% + 7% + 3% = 25%
Now find 25% of 420
Set up a proportion and cross multiply to solve.
25 * 420 = 10500
10500/100 = 105
The answer is 105 vehicles contained at least 3 people.
Hope this helped! :)
-Peredhel