#### Answer

$-4000$

#### Work Step by Step

Here, $C(x)=10,000+3x; R(x)=50x$
when the revenue breaks with the costs then $C(x)=R(x)$
Thus,
$10,000+3x=50x$
or, $10,000=50-30x$
or, $x=500$
Amount of profit function $P(x)=R(x)-C(x)$
or, $=50x-(10,000+3x)$
Thus, $P(x)=20x-10,000$
Now, $P(300)=20(300)-10,000$
or, $P(300)=-4000$