Two boxes are at rest on a smooth, horizontal surface. The boxes are in contact with

one another. If bor $1$is pushed with a force of magnitude F $=12\mathrm{.}00$N$,$the contact force between the

boxes is $8\mathrm{.}50$N; if$,$instead$,$ box $2$is pushed with the force F$,$the contact force is $3\mathrm{.}50$N$.$In either case, the boxes move together with an acceleration of $1\mathrm{.}70$m$/$s $.$

What is the mass of $($a$)$box $1$and $($b$)$box $2?$