Step-by-step explanation:
just think a little bit.
the balloon goes down 140 feet per minute.
how many feet will it have descended after 2 minutes ?
twice as much, right ?
after 5 minutes ? 8 minutes ? 10 minutes ? 15 minutes ?
we have to multiply.
simply because we need to maintain the value of the ratio feet/minute at all times.
so, when we multiply the "minute" part (by saying e.g. 5 minutes), we need to multiply the "feet" part with the same factor to keep the overall ratio the same. and then the resulting "feet" part gives us the answer.
so, after 2 minutes that means
140 ft / 1 min × 2/2 = 280 ft / 2 min
=> it descended 280 ft.
so, it's height is then at that moment
2520 - 280 = 2240 ft
5 minutes
140 ft / 1 min × 5/5 = 700 ft / 5 min
=> it descended 700 ft.
so, it's height is then at that moment
2520 - 700 = 1820 ft
and so on.
we see, that the general equation to determine the actual height (h) of the balloon depending on the passed number of minutes (m) is then
h = 2520 - 140m
so
2520 - 140×2 = 2240 ft
2520 - 140×5 = 1820 ft
2520 - 140×8 = 1400 ft
2520 - 140×10 = 1120 ft
2520 - 140×15 = 420 ft
