If RS = 8y + 4, ST = 4y + 8, and RT = 36, notice that RT is the line as a whole, so RS + ST = RT. The equation would be
8y + 4 + 4y + 8 = 36. Next, add like variables.
12y +12 = 36. Then, subtract 12 from 36.
12y = 24. Lastly, divide 24 by 12 and
y = 2
Hope that helps!