I assume that you mean: the length is 7cm more than the width, and the perimeter is 74 cm.
If so, we can write down the following system, where l and w represent, respectively, the length and the width:
![\begin{cases}l=w+7\\2(l+w)=74\end{cases} \iff \begin{cases}l=w+7\\l+w=37\end{cases} \iff \begin{cases}l=w+7\\(w+7)+w=37\end{cases}](https://img.qammunity.org/2020/formulas/mathematics/middle-school/w6qe4z5qgn7bhhmsm499u1qmhi9wsk1mss.png)
We can easily solve the second equation:
![(w+7)+w=37 \iff 2w+7=37 \iff 2w=30 \iff w=15](https://img.qammunity.org/2020/formulas/mathematics/middle-school/goxk9ez8kj77me0fr9bhk174xj13jdg3ec.png)
And finally solve for the length:
![l=w+7=15+7=22](https://img.qammunity.org/2020/formulas/mathematics/middle-school/1aak66n3qxlj4cr31otconr1eviexmmbo1.png)