The numerical length of ST is 8
A line segment is the part of a line joining two endpoints.
From the information given, we have that RT is a line segment and point S is between line R and T
We then have;
RT = RS + ST
Substitute into the formula;
4x + 9 = 2x + 7 + 5x - 7
collect like terms
4x - 7x = -9
-3x = -9
Make 'x' subject of formula
x = 3
Line ST = 5x - 7 = 5 (3) - 7 = 15 - 7 = 8
Thus, the numerical length of ST is 8
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