At 9:00 AM, the temperature started rising 2°F per hour until it reached 24°F at 2:00 PM. What was the temperature at 9:00 AM?

Step-by-step explanation:

I'm assuming that you are studying linear algebra right now.  If not, that's how I'm solving this, so bear with me.  

Let's start by saying that 9 am is time 0.  That means that

10 am is time 1

11 am is time 2

noon is time 3

1 pm is time 4

2 pm is time 5

Those times are the x values.  The only one we really need to worry about is the one given to us:  time 5, temp 24.  The temp is the y value, so the resulting coordinate is (5, 24).  We already know that the temp is steadily increasing 2 degrees per hour, so 2 is the slope of the line modeling this situation.  Using that info in the point-slope form of a line:

y - 24 = 2(x - 5) and

y - 24 = 2x - 10 and

y = 2x + 12

If 9 am is time 0, sub in a 0 for x and solve for y, the temp at 9 am:

y = 2(0) + 12 so

y = 12 degrees at 9 am.

( - 4 , -7 )

all the lines must parallel  

step-by-step explanation:

coordinates of c = ( - 1 , 2 )

3 units left = ( -4 , 2 )

9 units down = ( - 4 , 11 )