Xy=12
xdy/dx + y = 12
xdy/dx = 12 - y
dy/dx= (12-y) /x
dy/dx | x=-4 ,y=-3 = (12-(-3))/(-4)
= (12+3)/-4 = -15/4
Answer:
The costs of the plan are $0.15 per minute and a monthly fee of $39
Step-by-step explanation:
Let
x ----> the number of minutes used
y ----> is the total cost
step 1
Find the slope of the linear equation
The formula to calculate the slope between two points is equal to

we have the ordered pairs
(100,54) and (660, 138)
substitute


step 2
Find the equation of the line in point slope form

we have

substitute

step 3
Convert to slope intercept form
Isolate the variable y

therefore
The costs of the plan are $0.15 per minute and a monthly fee of $39
Answer:
question
Step-by-step explanation:
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10/8 or 5/4 or 1 1/4 or 1.25 or 125 percent.