So, the important information :
1. The first altitude which is = 250 feet
2. The rate of rise which is = 20 feet per minute
3. The equation of the altitude h after t minutes
h = 250 + 20 t
We can use this equation to find the altitude h after 5 minutes as following:
After 5 minutes, so t = 5
Substitute with t = 5 at the equation of the altitude h
So,
h = 250 + 20 * 5 = 250 + 100 = 350 feet