In the given figure, PQRS is a parallelogram with $\mathrm{PS}=7 \mathrm{~cm}, \mathrm{PT}=4 \mathrm{~cm}$ and $\text{PV}=5 \mathrm{~cm}$. What is the length of $\mathrm{RS}$ in $\mathrm{cm}?$ (The diagram is representative.)
- $\frac{20}{7}$
- $\frac{28}{5}$
- $\frac{9}{2}$
- $\frac{35}{4}$