If a machine requires $40$ tons of steel to produce $30$ tons of reinforced rods, the productivity of the machine is $\_\_\_\_\_.$

a$.$

$0\mathrm{.}75$

b$.$

$1\mathrm{.}50$

c$.$

$0\mathrm{.}67$

d$.$

$1\mathrm{.}33$