Answer:
34
Step-by-step explanation: if r is the midpoint then QR must be equale to RS
So the equation would be 5x-3=21-x
After solving this equation x=4
so you plug for instead of the x and for both QR and RS you get 17
so in order to dind QS you have to combine QR and RS
whuch means 17+17
and that equals to 34
