A block of mass $1\mathrm{.}86$ kg is placed on a frictionless floor and initially pushed northward, whereupon it begins sliding with a constant speed of $4\mathrm{.}19$ m$/$s$.$ It eventually collides with a second, stationary block, of mass $4\mathrm{.}22$ kg$,$ head$-$on$,$ and rebounds back to the south. The collision is $100\%$ elastic. What will be the speeds of the $1\mathrm{.}86-$kg and $4\mathrm{.}22-$kg blocks, respectively, after this collision?