Answer:
The value of QR is 12.
Explanation:
We are given that R is the midpoint of QS, and by definition of a midpoint we know that R is equidistant from the endpoints of segment QS. Therefore, we know that the length of QR is equal to the length of RS. Now we can form an algebraic equation with the values of the segments: 4x = x+9. Now we can subtract x from both sides of this equation to get 3x = 9. Now we can divide both sides by 3, to get that x = 3. Now we can plug this number into the expression 4x, to get the value of QR to be 12.