A single$-$threaded power screw is $25$ mm in diameter with a pitch of $5$ mm $.$ A vertical load on the screw reaches a maximum of $5$ kN $.$ The coefficients of friction are $0\mathrm{.}06$ for the collar and $0\mathrm{.}09$ for the threads. The frictional diameter of the collar is $45$ mm $.$ Find the overall efficiency and the torque to "raise" and "lower" the load.