For constant velocity (no acceleration) d = V*t
A) d horizontal = dh = Vh*t because there's no horizontal acceleration = Vcos(30)*t = 50*cos(30)*3 = 129.9 m
Force = m*a and there's gravity which is a force in the vertical direction so there IS acceleration in the vertical direction so we must use different equation.
(this comes from integrating acceleration*dt twice from calculus, but if u don't know calculus it's ok, just memorize this formula)
d = V0*t + 0.5*a*t^2 (note: if a is zero then u just get d = V0*t) in this case, gravity is accelerating in the opposite direction of motion (its pulling down but ur projectile is being shot up so you have to minus the acceleration). V0 would be 50*sin(30) to get the vertical velocity and a = -9.8 m/s^2.
d = 50sin(30)*(3 seconds) - 4.9*((3 seconds)^2) = 30.9 m in the vertical direction.