Answer
$C(x)=30x+85$
Work Step by Step
In a linear cost function, of the form
$C(x)=mx+b$,
the $m$ represents the marginal cost and
$b$ represents the fixed cost (zero units produced).
The graph of C(x) passes through the points
$(12, 445)$ and $(50, 1585).$
Slope: $m=\displaystyle \frac{1585-445}{50-12}=30$.
Point-slope equation:
$y-445=30(x-12)$
$y-445=30x-360\qquad/+445$
$y=30x+85$
or
$C(x)=30x+85$
