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  3)  16.2

Step-by-step explanation:

The supplement to the 115° angle on the right is 65°, the same as the angle at upper left. The vertical angles at C are the same measure, so this tells you that the two triangles FCB and ACD are similar by the AA similarity postulate. That being the case, corresponding sides are proportional:

  CB/CD = CF/CA

  CB = CD·CF/CA = 7.2·21.6/9.6

  CB = 16.2

When given two "point-to-point" triangles like this, quite often there is some sort of similarity relationship involved. First, you need to figure out what it is; then you need to make use of it as needed to answer the question being asked.

b. 153 students do not participate in sports and seventy-five 12th graders were surveyed