\left \{ {{3k+3s=24} \atop {2k+5s=25}} \right.
\left \{ {{k+s=8} \atop {2k+5s=25}} \right.
\left \{ {{k=8-s} \atop {2(8-s)+5s=25}} \right.
\left \{ {{k=8-s} \atop {16-2s+5s=25}} \right.
\left \{ {{k=8-s} \atop {3s=25-16}} \right.
\left \{ {{k=8-s} \atop {3s=9}} \right.
\left \{ {{k=8-s} \atop {s=3}} \right.
\left \{ {{k=8-3} \atop {s=3}} \right.
\left \{ {{k=5} \atop {s=3}} \right.