To find the length of line segment RT, you can use the segment addition postulate, which states that in a line segment, if you add the lengths of two smaller segments, it equals the length of the whole segment.
In this case:
ST = 7
RS = 5
To find RT, you can add ST and RS:
RT = ST + RS
RT = 7 + 5
RT = 12
So, the length of line segment RT is 12 units.