Answer
$C(x)=75x+550$
Work Step by Step
Assuming a linear cost function, $C(x)=mx+b$, where
m represents the marginal cost and
b represents the fixed cost.
Here,
$b$= $?\ \ $(fixed cost) and
$m$= $\$ 75$ (the cost to produce one item).
Let $C(x)=$ cost of producing $x$ items.
$C(x)=75x+b$
We don't know $b$, but we were given $C(50)=4300$ ,
so we solve (for $b$):
$75(50) +b=4300$
$3750+b=4300$
$b=550$
$C(x)=75x+550$
