In the figure, PQ is parallel to RS. The legth of RP is 4 cm; the length of PT is 16 cm; the length of QT is 20 cm. What is the length of SQ?

In the figure, PQ is parallel to RS, then
Consider triangles TPQ and TRS. These triangles are similar by AAA theorem, because
Then
[tex]\dfrac{TP}{TR}=\dfrac{TQ}{TS}.[/tex]
If PR = 4 cm and PT = 16 cm, then TR = TP + PR = 16 + 4 = 20 cm.
Thus,
[tex]\dfrac{16}{20}=\dfrac{20}{TS}\Rightarrow TS=\dfrac{20\cdot 20}{16}=25\ cm.[/tex]
Note that TQ + QS = TS, then QS = TS - TQ = 25 - 20 = 5 cm.
Answer: correct choice is A