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?

Gail is making costumes for a school play. each rabbit costume needs one and one half yards of white fur fabric, a yard of blue striped fabric, and a quarter of a yard of pink felt for the ears. g? ail needs to make eight rabbit man yards will she need, for the white fur fabric, blue striped fabric, and pink felt?