Total slices required for children,
[tex]C = \dfrac{40}{2}\times 1\\\\C = 20\ slices[/tex] .
Total slices required for adults,
[tex]A=\dfrac{2}{3}\times 60\times 2\\\\A = 80\ slices[/tex]
So, total slices required are, 20 + 80 = 100 .
Number of pizza, n = 100/8 = 12.5
So, he has to order 13 pizza cause pizza cannot be purchased in fraction.
Total price, P = 13 × 9 = $117 .
Hence, this is the required solution.