Trucks arrive at the loading dock of a wholesale grocer at the rate of $1\mathrm{.}2$ per hour. A single crew consisting of two workers can load a truck in about $30$ minutes. Crew members receive $$10$ per hour in wages and fringe benefits, and trucks and drivers reflect an hourly cost of $$62.$ The manager is thinking of adding another member to the crew. The service rate would then be $2\mathrm{.}4$ trucks per hour. Assume rates are Poisson. Use Table $1$ and Table $2.$

$10$

a$.$ Would the third crew member be economical? $($Round your intermediate and final answer to $2$ decimal places.$)$

b$.$ Would a fourth member be justifiable if the resulting service capacity were $3$ trucks per hour? $($Round your intermediate and final answer to $2$ decimal places.$)$