Answer:
At 1.5 seconds and 2.5 seconds
Step-by-step explanation:
Because this is parabolic motion, the object will reach the height of 68 feet when it's going up AND when it's coming down. In order to find out those times, you set the h on the left side of the equation equal to 68, because h stands for height.

Set that equal to 0 and factor to solve for t:

Using the quadratic formula, we get t = 1.5 and t = 2.5
Remark
All you need do is assume the small triangle is similar to the large one. MO:ML :: MP:MN must be solved.
Givens
MO = 28
ML = 28 + 14
MP = y
MN = y + 18
Equation
28:28+14 :: y: y + 18
Solve
28/42 = y / (y + 18)
28*(y + 18) = 42y Remove the brackets
28y + 18*28 = 42y
28y + 504 = 42y Subtract 28y from both sides.
504 = 42y - 28y
504 = 14y Divide by 14
504/14 = y
y = 36
It will be 23.2
just divide it if u have to round also do that