Answer:
10 is your answer
Step-by-step explanation:
Note each side length for each triangle.
RS = XY
ST = YZ
RT = XZ
Note the numbers given to each side. If one is equal to a number and the other side, then the side would be equal to the same number:
RS = 10 = XY ∴ XY = 10
RT = XZ = 7 ∴ RT = 7
ST = YZ = 9 ∴ ST = 9
~
