Given that
C(x)=0.005x3−0.02x2+30x+5000
The marginal cost is the instantaneous rate of change of total cost at any level of output.
∴ Marginal Cost at any x level of output = C′(x)
C′(x)=0.015x2−0.04x+30
Marginal Cost when 3 units are produced,
= C′(x) at x=3
= C′(3)
= 0.015(3)2−0.04(3)+30
= 0.135−0.12+30=30.015
Marginal Cost when 3 units are produced is 30.015.