х см длина
y см ширина
составим систему по условию
\left \{ {{x=3+y} \atop {x+y=11}} \right. <=> \left \{ {{x=3+y} \atop {3+y+y=11}} \right. <=> \left \{ {{x=3+y} \atop {2y=8}} \right. <=>\\\ <=> \left \{ {{x=3+y} \atop {y=4}} \right. <=> \left \{ {{x=7} \atop {y=4}} \right. " alt="\left \{ {{x-y=3} \atop {2(x+y)=22}} \right. <=> \left \{ {{x=3+y} \atop {x+y=11}} \right. <=> \left \{ {{x=3+y} \atop {3+y+y=11}} \right. <=> \left \{ {{x=3+y} \atop {2y=8}} \right. <=>\\\ <=> \left \{ {{x=3+y} \atop {y=4}} \right. <=> \left \{ {{x=7} \atop {y=4}} \right. " align="absmiddle" class="latex-formula">
7 см длина прямоугольника
4 см ширина прямоугольника