Answer: The length of SQ is 7 cm.
Explanation:
Since we have given that
Length of RP = 6cm
Length of PT = 18 cm
Length of QT = 21 cm
We need to find the length of SQ.
Since PQ is parallel to RS.
So, their ratio would be same anyhow.
So, it becomes,

Hence, the length of SQ is 7 cm.