Question

Someone please explain this to me please :)

Answer 1

R is the midpoint between points Q and S.
QR, which is a segment of the line, equals 5.
QS, which is the full line, equals 12.

To find RS, the remaining part of the line, you subtract 12 and 5.

The answer is 7 units.

Answer 2

QS is total distance. So assuming it is a linear and in one direction it is simple subtraction 12-5= 7