We know that RT=36 and that RS=2x+3 and ST=7x+6. We notice that

Then, plugging the corresponding values and expressions we have

Solving this equation for x,

Then te value of x is 3.
Once we have the value of x we are able to find the value of RS and ST, we just have to substitute said value in the expressions. Then

Therefore RS=9 and ST=27.