Circles with centers $P$, $Q$ and $R$, having radii 3, 4 and 5, respectively, lie on the same side of line $l$ and are tangent to $l$ at $P^{\prime }$, $Q^{\prime }$ and $R^{\prime }$, respectively, with $Q^{\prime }$ between $P^{\prime }$ and $R^{\prime }$. The circle with center $Q$ is externally tangent to each of the other two circles. What is the area of triangle $PQR$?