Answer:
RS + ST = RT
23 - 2x + 9x - 5 = 39
18 + 7x = 39
7x = 39 - 18 = 21
x= 21/7
x = 3
RS = 23 - 2x (given)
RS = 23 - 2(3)
= 23 - 6
RS = 17
