3)

[tex] \frac{9 + 11 + 3}{2} \times 7 = \frac{23 \times 7}{2} = \frac{161}{2} = 80.5[/tex]

4)

[tex] \frac{5 + 5 + 5}{2} \times 5 = \frac{15 \times 5}{2} = \frac{75}{2} = 37.5[/tex]