Drexel valves produces cast bronze valves on an assembly line. It currently produces $900$ valves using $400$ hours of machine and $500$ hours of labor. Its muDrexel valves produces cast bronze valves on an assembly line. It currently produces $900$ valves using $400$ hours of machine and $500$ hours of labor. Its multifactor productivity is:

$2$

$1\mathrm{.}8$

$2\mathrm{.}25$

$1$