Explanation:
At any point on the arrow's trajectory, the horizontal component of the velocity is the same. Therefore, the horizontal component of the velocity at the top of its trajectory is
[tex]v_x = v_{0x} = v_0\cos{42°} = (7.6\:\text{m/s})\cos{42°}[/tex]
[tex]\:\:\:\:\:=5.6\:\text{m/s}[/tex]