The formula is 700 - 100 - 75(n-1), where n is the number of months.
X=18y
Y=0
Hope this helps :)
The answer is going to be 14 15 16
14+15+16 = 45
a) because it is equal to the area of the shaded region between X=4 and X=6, and the probability that X falls within some interval is given by the area under the PDF.
b) because the shaded region is a rectangle of height 1/5 (by virtue of X following a uniform distribution over the interval [2, 7], which has length 5).
Your plane is 3x-y+4z=32 and you want to know when it crosses the z-axis or in other words intersects it. Along the z axis only z changes, additionally it goes through the origin (0,0,0).
So we can insert x=y=0 into the plane to calculate the point along the z-axis where it intersects the plane:
3x-y+4z=32
insert 0s:
4z=32
z=8
so the solution plane intersects the z-axis at (0,0,8)