Answer:
4 seconds.
Explanation:
The function f(x)=-10(x)(x-4) ........ (1), represents the approximate height of a projectile launch on the ground into the air as a function of time in seconds x.
Now, we are asked that for how long from the launch does the projectile stays in the air.
Therefore, we have to solve the equation (1) making f(x) as zero.
Hence, 10x(x - 4) = 0
⇒ x = 0 or x = 4
(As x can not be zero since at x = 0 sec, the projectile was at the ground.}
Hence, x = 4 seconds.
Therefore, the projectile was in the air for 4 seconds. (Answer)