Given
The projectile is in air for a time of t=8 sec
To find
The time it takes to reach the highest point
Step-by-step explanation
A projectile moves up to the highest point and then again moves down following a parabolic path.
So it will reach the highest point at a time half the time it requires to follow teh parabolic path.
The time taken to reach the highest point is 4 sec
Conclusion
The time taken is 4 sec.