The value of ST is 21
Note that line S, U and T are points in a line segment
From the information given, we have that;
ST = TU
Where;
Substitute the values into the equation
3x + 3 = 2x + 9
collect like terms
3x - 2x = 9 - 3
Subtract like terms
x = 6
But we have that ST = 3x + 3 = 3(6) + 3 = 18 + 3 = 21
Thus, the value of ST is 21
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