Check the picture below. You can pretty much count the units off the grid for its width and length.
A slice of a right rectangular pyramid parallel to its basesince parallel to the base it should have the same figure to the base which is rectangle.
a slice of a right square pyramid perpendicular to its base but not through its top vortex. since not to the vortex, it will form a trapezoid
a slice parallel to the base of a right rectangular prism with a square basesince parallel to the base it should have the same figure to the base which is square
For 21 go on your calculator and use either the y= or the table button to type in your formula and find the x values where y is 0 using a graph or a table. For 22 the answer is 13 because a square root must be of a positive number and x-12 is positive at x=13 but not x=8.