Final answer:
The elevation of the balloon at 10 seconds is 180 feet.
Step-by-step explanation:
The elevation of the balloon is modeled by the function h(x) = -6x + 240, where x is the time (in seconds) since you first noticed the hot air balloon. To find the elevation at 10 seconds, substitute x = 10 into the equation:
h(10) = -6(10) + 240 = -60 + 240 = 180 feet