the sum of 12 and a number/n
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
-2x < = 3x + 1 < = 10
split them
-2x < = 3x + 1 3x + 1 < = 10
-2x - 3x < = 1 3x < = 10 - 1
-5x < = 1 3x < = 9
x > = -1/5 x < = 3
solution is : -1/5 < = x < = 3 <==