With the information given we have:

Where W is the weight, k is the proportionality constant and r is the radius of the can's radus. Remember that the weight varies jointly so this key word means that you need to multiply the mentiones parameters by a proportionality constant k.
We simply need to reorganize the expression and isolate k for the frst answer:

Replacing by all the appropiate values we get:

For the second part knowing k we have:
Answer:
-4 + -4x
Step-by-step explanation:
Simplifying
3x + -7x + -4
Reorder the terms:
-4 + 3x + -7x
Combine like terms: 3x + -7x = -4x
-4 + -4x
Answer:
The maximum revenue will be
at price 
Step-by-step explanation:
Given:

Find the vertex of the parabola represented by given equation:

When
then

The maximum revenue will be
at price 