1. Three smooth spheres $P,QandR$ with masses 20 kg, 35 kg and $m$ kg respectively, are travelling in the same direction along a straight line with speeds $7m{s}^{-1},um{s}^{-1}and10m{s}^{-1}$.

Given that $P,QandR$ all have the same momentum, find

(i) the value of $m$,

(ii) the value of $u$.