Answer
Please see the work below.
Work Step by Step
We know that
$t=\sqrt{\frac{2h}{g}}$
We plug in the known values to obtain:
$t=\sqrt{\frac{(2)(1.9)}{9.8}}=0.623s$
Now we can find the horizontal speed as
$v=\frac{x}{t}$
We plug in the known values to obtain:
$v=\frac{4.5}{0.623}=7.2\frac{m}{s}$
