Question 311461
Suppose that the remaining distance to drive (in miles) is a linear function of
 his driving time (in minutes). 
When graphed, the function gives a line with a slope of -0.9
Jim has 74 miles remaining after 31 minutes of driving.
:
Use the form mx + b = y; y=dist, x=minutes; m=-.9
When x = 31 and y = 75, find b
-.9(31) + b = 74
-27.9 + b = 74
b = 74 + 27.9
b = 101.9; 
then: y = -.9x + 101.9 is the equation, a graph of this looks like this
{{{ graph( 300, 200, -10, 90, -20, 125, -.9x+101.9) }}}
:
 How many miles were remaining after 19 minutes of driving?
y = -.9x + 101.9
x = 19 mi
y = -.9(19) + 101.9
y = -17.1 + 101.9
y = 84.8 miles remaining after 19 min