Answer
$R=(20t+2.48)lb$
Work Step by Step
We know that:
$\Sigma F=m\frac{dm}{dt}+v_{D/i} \frac{dm_i}{dt}$
$\implies R-w(vt)=(0-v(\frac{wv}{g}))$
$\implies R=wv(t-\frac{v}{g})$
We plug in the known values to obtain:
$R=5(4)(5-\frac{4}{32.2})$
This simplifies to:
$R=(20t+2.48)lb$
