# Linear Functions Help

• Mar 6th 2008, 08:22 PM
eraser851
Linear Functions Help
Could I get some help with this math problem? I'm a complete idiot when it comes to math.

The cost of water use (in dollars) is a linear function of the amount of water used (in hundreds of cubic feet, HCF), as shown in the figure below. The cost for using 14 HCF of water is $39.40, and the cost for using 28 HCF is$63.90. What is the cost for using 19 HCF of water?
http://img.photobucket.com/albums/v2...rfunctions.jpg

No clue on how to solve this.

• Mar 6th 2008, 08:39 PM
TheEmptySet
Quote:

Originally Posted by eraser851
Could I get some help with this math problem? I'm a complete idiot when it comes to math.

The cost of water use (in dollars) is a linear function of the amount of water used (in hundreds of cubic feet, HCF), as shown in the figure below. The cost for using 14 HCF of water is $39.40, and the cost for using 28 HCF is$63.90. What is the cost for using 19 HCF of water?
http://img.photobucket.com/albums/v2...rfunctions.jpg

No clue on how to solve this.

I don't think your post is in the right forum...

Given that data we can make two ordered pairs (14,39.40) and (19,63.90)

using these two point we can find the slope m.

$m=\frac{63.90-39.40}{19-14}=\frac{24.50}{5}=4.9$

We can then use the slope we just calculated and one of our ordered pairs to find the equation of the line.

$y-39.40=4.9(x-14)$

we can use this equation to find the value for y when x=19.

Good luck.