Please read the attached file
Answer:
The first set of ordered pairs is a function, because no two ordered pairs have the same first coordinates with different second coordinates. The second example is not a function, because it contains the ordered pairs (1,2) and (1,5).
Hope this helps you with your question.
I assume that you meant RS and ST are segments of RT. If that is true then:
RS+ST=RT, using the values for these given...
8y+4+4y+8=36 combine like terms on left side
12y+12=36 subtract 12 from both sides
12y=24 divide both sides by 12
y=2