<u>Direct Variation:</u> 

when y = 7: 
14 = 15x

<u>Inverse variation:</u> y*x = k
15 * 2 = k
30 = k
when y = 7: 7 * x = 30

The answer to this is x < -10/7
To answer this item, we have 4 as the speed of the kayaker in still water and the speed of current be y.
When the karayaker moves upstream or against the current, his speed would be 4 - y. Further, if he moves downstream or with the current, the total speed would be 4 + y. The time utilized for the travel is equal to the ratio of the distance and the speed.
Total time = 9/(4 - y) + 9/(4 + y) = 6
We multiply the equation by (4-y)(4+y)
9(4-y) + 9(4 + y) = 6(4-y)(4+y)
Simplifying,
72 = 96 - 6y²
Transposing all the constants to only one side of the equation and rearranging,
6y² = 96 - 72
y² = 4
y = 2
Hence, the speed of the river's current is 2 miles/hr. <em>The answer is letter B.) 2 miles/hour.</em>
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