How do you find the length of SU in the isosceles trapezoid?

If this is an isosceles trapezoid, the triangles ΔSWV and ΔTWU must be congruent. Then, the corresponding sides are congruent too:
[tex]\begin{gathered} TW\cong SW \\ UW\cong VW \end{gathered}[/tex]From the given information, we can say that:
[tex]UW=3[/tex]Additionally, we know that:
[tex]SU=SW+UW[/tex]Finally, using the values of SW and UW:
[tex]\begin{gathered} SU=1.7+3 \\ \\ \therefore SU=4.7 \end{gathered}[/tex]