Solve the Problem $R(t)=2 \sqrt{x}$ , Where $x$ Is the Number of Units Produced and Sold

Solve the problem.
-A product sells by word of mouth. The company that produces the product has noticed that revenue from sales is given by $R(t) =2 \sqrt{x}$ , where $x$ is the number of units produced and sold. If the revenue keeps changing at a rate of $\$ 700$ per month, how fast is the rate of sales changing when 300 units have been made and sold? (Round to the nearest dollar per month.)

A) $\$ 48,497 /$ month
B) $\$ 40 /$ month
C) $\$ 12,124 /$ month
D) $\$ 6062 /$ month