Answer:
The credit remaining on a phone card is 16.36 dollars
Explanation:
A linear function is a polynomial function of the first degree of the form:
f (x) = m * x + b or y = m * x + b
where m is the slope of the linear function and b is the ordinate to the origin and it is the coefficient of the independent variable.
Given the coordinates of two points (x1, y1) and (x2, y2), you can determine the slope of the linear function using the following formula:
The coefficient b is calculated simply by replacing any of the points in the linear function, knowing m, and isolating the value.
In this case you want the linear function first:
credit remaining on a phone card= m* the calling time in minutes + b
Being the points (32; 21.16) and (56;18.28), then the slope m will be:
m= -0.12
Then, replacing the point (32; 21.16) in
credit remaining on a phone card= -0.12* the calling time in minutes + b
you get:
21.16= -0.12*32 + b → 21.16= -3.84 + b → 21.16 + 3.84= b → 25=b
Then, replacing the point (56;18.28) in
credit remaining on a phone card= -0.12* the calling time in minutes + b
you get:
18.28= -0.12*56 + b → 18.28= -6.72 + b → 18.28 + 6.72= b → 25=b
You can see that the value of b is the same.
So the linear function is:
credit remaining on a phone card= -0.12* the calling time in minutes + 25
Being the call time in minutes equal to 72, you replace this value in the linear function:
credit remaining on a phone card= -0.12* 72+ 25
and you get:
credit remaining on a phone card= -8.64+ 25
credit remaining on a phone card= 16.36
The credit remaining on a phone card is 16.36 dollars