Question

A water balloon is catapulted into the air so that it's height, in meters, after t seconds is h = -4.9t^ +27t +2.4

Answer 1

$h = -4..9t^2+27t+2.4\ for\ t=3$

Just replace t with 3 and solve.

$h = -4.9*3^2 + 27*3 + 2.4 \\ h = -4.9*9 + 27*3 + 2.4 \\ h=-44.1 + 81 + 2.4 \\ \boxed{h=39.3}$