Evaluate the expression below for x = 9. 3x + 4 • |x - 8| - 14

y = 0.45x + 21

Step-by-step explanation:

let x represent the number of minutes used in a month.

Let y represent the monthly cost for x minutes.

If we plot y on the vertical axis and x on the horizontal axis, a straight line would be formed. The slope of the straight line would be

Slope, m = (304.5 - 183)/(630 - 360)

m = 121.5/270 = 0.45

The equation of the straight line can be represented in the slope-intercept form, y = mx + c

Where

c = y intercept

m = slope

To determine the y intercept, we would substitute x = 360, y = 183 and m = 0.45 into y = mx + c. It becomes

183 = 0.45 × 360 + c

183 = 162 + c

c = 183 - 162

c = 21

The equation for the monthly cost is

y = 0.45x + 21