What is a reciprocal for numbers it sounds realy confusing

For the following geometric sequence, find the recursive formula. {-80, 20, -5, } i need : ')

Aprojectile is thrown upward so that its distance above the ground after t seconds is given by the function h(t) = -16t2 + 704t. after how many seconds does the projectile take to reach its maximum height?

Bob the builder is making 480kg of cement mix. this is made by cement, sand and gravel in the ratio 1: 3: 4