20. SR = 17
22. TR = 5 and PR= 10
23. ST=9.5
24. X=1.5
for 23, the length of QS is 19, and ST is half of that length. so you divide 19/2 and get 9.5
for 24, i found it difficult to explain but i included a picture of my work. i know it may not help but it's all i've got.