Here v = final velocity
u = initial velocity
a = acceleration
t = time
s = distance

You must remember above three equation.

For above problem
acceleration is gravity i.e. g = 9.8m^2/s
initial velocity u = 0
time t = 3 sec

We apply second equation
s = 0 x 3 + 1/2 x 9.8 x 3
s = 1/2 x 9.8 x 3
s = 14.7 m

For second problem
Use trigonometry equation

/
/
/ 500 m/s
/
/_30 deg_____________

For horizontal velocity
sin 30 deg = v(hor)/v
or
v(hor) = v x sin 30 deg
= 500 x (square root 3)/2
= 433 m/s

For vertical velocity
cos 30 deg = v(vert)/v
or
v(vert) = v x cos 30 deg
= 500 x 1/2
= 250 m/s