Math help-Linear Function#3

1
Write a linear function using the data for 3- and 9-month-old girls.

Age (months) Height (inches)
3 23.5
6 25.6
9 27.5
#2 Use your model to find the height of a 15 year old girl, to the nearest foot.
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The problems above have already been solved in previous questions I've asked..
If you haven't solved these problems please do and answer the following question please:

Based on your (my) answer,what can you conclude about the linear model?
Good explanation.Thank you guys!

It's me again...

the linear model is considered as increasing function. why?
because as x increases, y also increases and once x decreases ...y also decreases.

the 2nd given 6, 25.6 --> 25.6 must be 25.5 to have a fixed fist difference in y's, to call it linear function

A linear model would be something close to h = (2/3) a + 21.5, where h is the height in inches and a is the age in months.

15 years is 180 months, so we'd predict a height of around (2/3) (180) + 21.5 = 141.5 inches, or 12 feet to the nearest foot. So we can conclude that the linear model is not valid over this range.