\(\begin{array}{c|c}
\text{Quantity of singlets} & \text{Short run total costs(N)} \\
0 & 1,000 \\
10 & 1,200 \\
20 & 1,400 \\
30 & 1,600 \\
40 & 1,800 \\
\end{array}\)

The short run total costs for different levels of output for a firm producing singlets are shown above. Calculate the variable cost per unit at an output of 20.