Aprojectile is thrown upward so that it's distance above the ground after t seconds is h=-16t^2 +672t. after how many seconds does it reach its maximum height?

21 seconds

Step-by-step explanation:

We know that a parabola with equation attains its maximum height at :-

The given function:

It will attain its maximum height at :

Hence , after 21 seconds the projectile will reach its maximum height .

135 is your answer

step-by-step explanation:

try 180 times three then divide that number by 4 (sides) to get your answer. im glad to : )