Find an Equation for the Rational Function Graph $C ( x )$

Multiple Choice

Find an equation for the rational function graph.
-If the average cost per unit $C ( x )$ to produce $x$ units of plywood is given by $C ( x ) = \frac { 900 } { x + 30 }$ , what is th unit cost for 50 units?

A) $\$ 18.00$
B) $- \$ 12.00$
C) $\$ 11.25$
D) $\$ 0.60$