A cloud service provider is implementing a dynamic load balancing algorithm to

improve the handling of incoming user requests during peak usage times. The

function $f(x)=x(0\mathrm{.}4x+71{)}^{(\frac{1}{2})}$ models how the network's efficiency, in terms of

requests handled per second, scales as $x$ additional servers are brought online.

Determine the rate of efficiency when $x=18.$ Write only a number as your answer

and round to $1$ decimal place.