How to interpret marginal effects in stata?

Consider the integral: 4 0 16 − y2 − 16 − y2 4 1 x2 + y2 dz dx dy . (a) describe w. use the standard view of the x, y, and z axes. front half of a cone with a rounded top. full cone with a flat top. right half of a cone with a flat top. front half of a cone with a flat top. right half of a cone with a rounded top.

One side of a rectangle is 7 feet shorter than seven times the other side. find the length of the shorter side if we also know that the perimeter of the rectangle is 306 feet.

How do you use the elimination method for this question? explain, because i really want to understand!