You can use the distance formula to find the distance between any two points ion the plane. In this case, look carefully at the coordinates:
R(-1, 7) and T(-7, 7), Notice they both have y-coordinate 7. That means they are both on the same horizontal line. To find their distance, just subtract -7 from -1 and take the absolute value.
|-1 - (-7)| = |-1 + 7| = |6| = 6
The distance is 6 units
So your equation is

. You need to simplify this answer.
So first off, do 2x times 2x.
2 x 2 = 4.
Your equation is now

You're already off to a great start, so now let's add 4x + 7x. It is 11x.
Your equation is almost done! It's

right now.
Divide both sides by 11, and your answer is...
0.36363636 and so on, or you can round to the nearest hundreth, in which it will be
0.36.
I hope I helped!