A ball is thrown straight down from the top of a 300ft build

(A ball is thrown straight down from the top of a 300-ft building with an initial velocity of -12 ft/sec. the height of the ball above the ground is given by the function s(t)=-16t^2-12t+300.find the instantaneous velocity of the ball when it is 246ft above the ground

v(final)=v(initial)+at ...that is final velocity equals initial velocity plus acceleration due to gravity times the time.