S would be the annual sales of the electronic device. In this case, that number is in the millions.
Therefore, our 13.9 becomes 13.9 millions.
Or written out, it would be: 13,900,000
You do the implcit differentation, then solve for y' and check where this is defined.
In your case: Differentiate implicitly: 2xy + x²y' - y² - x*2yy' = 0
Solve for y': y'(x²-2xy) +2xy - y² = 0
y' = (2xy-y²) / (x²-2xy)
Check where defined: y' is not defined if the denominator becomes zero, i.e.
x² - 2xy = 0 x(x - 2y) = 0
This has formal solutions x=0 and y=x/2. Now we check whether these values are possible for the initially given definition of y:
0^2*y - 0*y^2 =? 4 0 =? 4
This is impossible, hence the function is not defined for 0, and we can disregard this.
x^2*(x/2) - x(x/2)^2 =? 4 x^3/2 - x^3/4 = 4 x^3/4 = 4 x^3=16 x^3 = 16 x = cubicroot(16)
This is a possible value for y, so we have a point where y is defined, but not y'.
The solution to all of it is hence D - { cubicroot(16) }, where D is the domain of y (which nobody has asked for in this example :-).
(Actually, the check whether 0 is in D is superfluous: If you write as solution D - { 0, cubicroot(16) }, this is also correct - only it so happens that 0 is not in D, so the set difference cannot take it out of there ...).
If someone asks for that D, you have to solve the definition for y and find that domain - I don't know of any [general] way to find the domain without solving for the explicit function).
The average rate of change of a graph between two intervals is given by the difference in value of the values on the graph of the two interval divided by the difference between the two intervals.
Part A.
From the graph the average Valentine's day spending in 2005 is 98 while the average Valentine's day spending in 2007 is 120.
The average rate of change in spending between 2005 and 2007 is given by

Part B
From the graph the average Valentine's day spending in 2004 is 100 while the average Valentine's day spending in 2010 is 103.
The average rate of change in spending between 2004 and 2010 is given by

Part C:
From the graph the average Valentine's day spending in 2009 is 102 while the average Valentine's day spending in 2010 is 103.
The average rate of change in spending between 2009 and 2010 is given by
The answer is D because to use Pythagorean Theorem it has to be a right triangle.
41.3 is your answer because when you divide 496 and 12 you get 41.3 and therefore 49.6 divided by 1.2 is 41.3 so they both calculate 1 decimal