Answer:
The instantaneous velocity after eight seconds is 9 m/s
Step-by-step explanation:
Given as :
The ball shot upward with velocity of 15 m/s
The height of the ball after t sec is given as h(t) =
Now, The instantaneous velocity after 8 sec = 
Or, The instantaneous velocity =
or, The instantaneous velocity = 
Now at t = 8 sec
The instantaneous velocity = 5 + 4 = 9 m/s
Hence The instantaneous velocity of ball at t = 8 sec , is 9 m/s Answer
The question is -x/3 = 2 which is 1/3x=2
multiply both sides by 3, and you'll get x = 6