check the picture below.
notice, a function that is decreasing, namely have a negative slope, doesn't have to be negative.
Answer:15
Step-by-step explanation:
Given
Craftsman sell 10 Jewelry set for $500 each
For each additional set he will decrease the price by $ 25
Suppose he sells n set over 10 set
Earning
Earning 

differentiate to get the maximum value

Equate
to get maximum value



Thus must sell 5 extra set to maximize its earnings.
Answer:
(Choice C) C Replace one equation with a multiple of itself
Step-by-step explanation:
Since system A has the equations
-3x + 12y = 15 and 7x - 10y = -2 and,
system B has the equations
-x + 4y = 5 and 7x - 10 y = -2.
To get system B from system A, we notice that equation -x + 4y = 5 is a multiple of -3x + 12y = 15 ⇒ 3(-x + 4y = 5) = (-3x + 12y = 15).
So, (-x + 4y = 5) = (1/3) × (-3x + 12y = 15)
So, we replace the first equation in system B by 1/3 the first equation in system A to obtain the first equation in system B.
So, choice C is the answer.
We replace one equation with a multiple of itself.
Inequality:
5x - 3 ≤ 28
Answer:
5x - 3 <span>≤ 28
5x </span><span>≤ 31
x </span><span>≤ 31/5 or 6.2 ($6.20)</span>