Use the position function s(t) = -16t^2 + 1000, which gives the height in feet of an object that has fallen for t seconds from a height of 1000 feet. the velocity at time t = a seconds is given by:

lims(a) - s(t)

t to a a - t

if a construction worker drops a wrench from a height of 1000 feet, how fast will the wrench be falling after 5 seconds?

the answer is 160ft/sec

but i am not sure how to get there,

this is what i have so far:

-16 * 5^2 +1000 = 600

600 - (-16t^2 + 1000)5 - t

where do i go from here? please help!