\[
\boxed{
 \left\{ {\frac {\rm d}{{\rm d}t}}x \left( t \right) + \left( ax \left( t \right) +by \left( t \right)  \right) f \left( t \right) =g \left( t \right) ,{\frac {\rm d}{{\rm d}t}}y \left( t \right) + \left( cx \left( t \right) +dy \left( t \right)  \right) f \left( t \right) =h \left( t \right)  \right\} }
\]