Answer:
4.52secs
Explanation:
Given the height of a falling object expressed as;
d=3t+5t^2
If the object travel 84 feet, we are to find the time t it takes to travel. On substituting;
84 = 3t+5t^2
3t+5t^2 - 84 = 0
t = -5±√25-4(3)(-84)/2(3)
t = -5±√25+1008/6
t = -5±32.14/6
t = -5+32.14/6
t = 27.14/6
t = 4.52 secs
Hence it will take 4.52secs for the object to travel 84feet