Please help me with geometry problem, I don't understand Ik the answer is RS=97 but please teach me the steps?

We're given:
RS = 5x+17
ST = 8x-31
S is the midpoint of line RT

So,
     RS = ST            ← By the definition of midpoint
5x+17 = 8x-31        ← By substitution ... Now, solve for x
17+31 = 8x-5x
      48 = 3x
        x = 16            ← Now, to get the value of RS, substitute this into the equation that defines RS

RS = 5x+17
RS = 5*16 + 17
RS = 80 + 17
RS = 97                 ← ANSWER

Have a good one!
    

5x + 17 = 8x - 31
48 = 3x
x = 16

RS = 80 + 17 = 97

97