18. Determine the volume of the figure bounded by the following planes. z=3 z = -8 Z x - 2y = 6 4x + y = -15 x + y = -2

Suppose that candy costs $4 per pound and cashews cost $5 per pound. Let x be the number of pounds of candy bought and y be the number of pounds of cashews bought.  Graph the region in the xy-plane that represents all possible weight combinations of candy and cashews that cost less than or equal to $20.

9. Find the volume of the solid in the first octant enclosed by the surface z = -x² and the four planes x = 2, y = 3, y = 0, z = 0.

Find the volume of the parallelpiped R³ whose corner points are (0, 0, 0), (1, 1, 1), (2, 2, 5), (1, 3, 3) and their sums.