a)
[tex] \frac{(8 + 11) \times 4}{2} = \frac{19 \times 4}{2} = 19 \times 2 = 38[/tex]
b)
[tex] \frac{(3 + 6) \times 3}{2} = \frac{9 \times 3}{2} = \frac{27}{2} = 13.5[/tex]
c)
[tex] \frac{(6 + 4) \times 7}{2} = \frac{10\times 7}{2} = \frac{70}{2} = 35[/tex]
