Automan,Inc The Desired Output Rate Is 50 Robots an Hour

Multiple Choice

Automan,Inc.makes "tennis robots" on an assembly line with 9 tasks.The tasks and their times follow.
$$\begin{array} { | c | c | } \hline \begin{array} { c } \text { Work } \\\text { Element }\end{array} & \begin{array} { c } \text { Time } \\( \mathrm { sec } ) \end{array} \\\hline 1 & 20 \\2 & 30 \\3 & 25 \\4 & 25 \\5 & 10 \\6 & 20 \\7 & 15 \\8 & 45 \\9 & 50 \\\hline\end{array}$$
The desired output rate is 50 robots an hour.The "theoretical maximum efficiency" on the line is

A) less than 85%.
B) more than 85% but less than or equal to 90%.
C) more than 90% but less than or equal to 95%.
D) more than 95%.