We know that, Profit = Sales - Cost
In January Profit is = $(30-28) = 2$
Number of employees in January = $10$
∴ Profit per employee in January = $\dfrac{2}{10} = \dfrac{1}{5} =0.2$
In March Profit is = $(35-30) = 5$
Number of employees in March = $12$
∴ Profit per employee in March = $\dfrac{5}{12} = 0.4166 $
In July Profit is = $(37-35) = 2$
Number of employees in July = $15$
∴ Profit per employee in in July = $\dfrac{2}{15} = 0.133$
In September Profit is = $(39-37) = 2$
Number of employees in September = $16$
∴ Profit per employee in September = $\dfrac{2}{16} = 0.125$
∴ March has the highest profit per employee .