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