In an extensive study of cost functions for 40 firms in Great Britain, it was found that if $\displaystyle {x}$ is the output (in millions of units) and $\displaystyle {y}$ is the total cost (in thousands of pounds of sterling), then the cost function is similar to the following:
$\displaystyle {C}{\left({x}\right)}=-{0.02}{x}^{{2}}+{2.23}{x}+{14.66}$
Compute the marginal costs when $\displaystyle {x}={28}$ million units have been produced.


The marginal costs at $\displaystyle {28}$ million units is (Enter a number only, including a negative sign, if appropriate.)

The proper units are: