You need to add a -1
We can find this by setting up the equation like so
x + (-6) + 12 + 15 / 4 = 5
x + 21 = 20
x = 20 -21
x = -1
Now if we insert -1 where x is located in the equation, you will get a means of 5
In general, the sum of the measures of the interior angles of a quadrilateral is 360. This is true for every quadrilateral. This does not help here, because there are two angles (angles B and D) we know nothing about. We only know about opposite angles A and C.
In this case, you can use another theorem.
Opposite angles of an inscribed quadrilateral are supplementary.
m<A + m<C = 180
3x + 6 + x + 2 = 180
4x + 8 = 180
4x = 172
x = 43
m<A = 3x + 6 = 3(43) + 6 = 135
Answer: 135 deg
Consider the top half of a sphere centered at the origin with radius

, which can be described by the equation

and consider a plane

with

. Call the region between the two surfaces

. The volume of

is given by the triple integral

Converting to polar coordinates will help make this computation easier. Set

Now, the volume can be computed with the integral

You should get
Answer: -2/3
3-(-1) over
-2-4
This equals 4/-6 which reduces to -2/3