Jon S. answered 08/14/20
Patient and Knowledgeable Math and English Tutor
By the segment addition rule, length of ST + length TU equals length of SU so
3x -1 + 3x = 4x + 1
6x - 1 = 4x + 1
2x = 2
x = 1
substituting value of x back into formula for length of SU: 4(1) + 1 = 5