"a projectile is launched in the air according to the equation h(t)= -16t^2 + 125t + 5. at what time does the projectile land? " and how do i do problems like these! ?

"according to the equation is a sloppy description, and announces that whoever said it or wrote it doesn't really have a clue to what the equation means or what it's good for.

h (t) is the HEIGHT of the projectile above the ground at any time 't'. When the projectile hits the ground, h (t) is zero. Write that ! Then you have a quadratic equation that you can easily solve for 't'.