Answer
$$\color{blue}{\bf{[300, \infty)}}$$
Work Step by Step
Remember that the break even point is where the revenue, $R$ is greater than or equal to the costs, $C$, or simply:
$$R\geq{C}$$
Simply plug in the values and work the inequality
$8x\geq{3x+1500}$
subtract $3x$ from both sides
$5x\geq{1500}$
divide by $5$
$x\geq{300}$
The break even point is $300$ units or more, or in interval form:
$\color{blue}{\bf{[300, \infty)}}$
