Yolanda is a software saleswoman. Let y represent her total pay (in dollars). Let x represent the number of copies of 'English is Fun' she sells. Suppose that x and y are related by the equation y=1900+80x.

a. What is the change in Yolanda's total pay for each copy of 'English is Fun' she sells?

b. What is Yolanda's total pay if she doesn't sell any copies of 'English is Fun'?

Answer: a) $80 b) $1900

Step-by-step explanation:

a) change in Yolanda total pay y, for each 'English is fun' sold x, i. e ∆y/∆x = dy/dx

y = 1900+80x

differentiating the equation above

dy/dx = 80

Therefore, dy/dx = $80

change in Yolanda total pay y, for each 'English is fun' sold x, is $80

b) if she doesn't sell any copy of ' English is fun ', x=0

Therefore,

y = 1900 + 80x

Substituting x = 0, into the equation above

y = 1900 = $1900

Therefore her total pay is $1900 if she did not sell any ' English is fun'