Suzy stands on the talahatchee bridge kicking stones into the water below. if she kicks a stone with a horizontal velocity of 3.50 m/s, and it lands in the water a horizontal distance if 5.40 m from where she is standing, how high is the bridge. can you me thus us 2-d motion

Yep.  I think I can.

Horizontal motion doesn't speed up or slow down.
 
                              distance                 =  (speed) x (time)

                                5.4 m                   = (3.5 m/s) x (time)
Divide each side
by  3.5 m/s:              (5.4 m) / (3.5 m/s)  =                 time

                               time  =  1.543 seconds   (rounded) .

That's how much time the stone took to fall from the bridge to the water.

Now we can go on to the vertical distance:
Do you remember this physics formula for falling distance ?

                    Distance  =  (1/2) (gravity) (time)²

                   Distance   =  (1/2) (9.8 m/s²) (1.543 sec)²

                                   =    (4.9 m/s²)    x    (2.38 sec²)

                                   =        11.7 meters .