Which is the x value and which is the y value

When data is presented in a table like this, the x-value (independent variable) is usually the one on the left.

The y-value (dependent variable) is usually the one on the right. (This is the assumption made by spreadsheet programs that do graphing.)

_____

The slope of the graph is the difference of a pair of y-values divided by the difference of the corresponding pair of x-values. These graphs both include the point (0, 0), so you can draw the graph once you know the slope.

39) ∆y/∆x = (4.5 -3)/(3 -2) = 1.5/1 = 1.5 . . . . the slope of the line

... y = 1.5x . . . . . the equation of the line

... y = 1.5×25 = 37.5 . . . . the height of 25 pieces (inches)

40) ∆y/∆x = (474 -237)/(6 -3) = 237/3 = 79 . . . . . the slope of the line

... y = 79x . . . . . the equation of the line

... y = 79×30 = 2370 . . . . the cost for 30 nights (dollars)

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step-by-step explanation:

this is a direct variation proportion. y = kx

y is the total amount due, k is the constant of variation, and x is the number of texts sent.

plug in the 3.20 and the 16 to solve for the "k". this is the constant of proportionality. it is the value that will not change.

3.20 = k(16). solving you get $.20 per text.

the equation would then be y = .20x