A student making an apple sorting machine decides to make use of a conveyor belt to transport the apples from one

point in the sorting machine to another. The corveyor belt rolls over $2$ pulleys which must rotate at the same speed.

The shaft of the driver pulley is connected to a motor which runs at $60$ rpm $.$

The apples may not move faster than $1\mathrm{.}2$ m in $7$ seconds.

Determine the diameter, in mm$,$ of the pulleys required for this conveyor belt