The height about the ground of an object t seconds after it

The height about the ground of an object t seconds after it is launched vertically upward is h(t)=100t-5t^2 meters
What is the velocity of the object after 3 seconds

Solution

h\'(t) = 100 - 10t
h\'(3) = 70 m/sec
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Did you mean to ask the height? If so,
h(3) = 100*3 - 5*9
h(3) = 255 meters, going up at 70 meters/sec