In 1998 the U.S. Hispanic high school dropout rate was 29.5% and in 2008 it had dropped to 18.3%. Let d (the outputs) represent the U.S. Hispanic high school dropout rate and y (the inputs) represent the years since 1990. Find a linear model for the dropped rate given the year.

linear model is given by y=mx+c, where m is the slope and c is the intercept.
From the information given, let 1998 be our starting point, 0. 2008 will be time,x=2008-1990=18
therefore our points will be:
(0, 0.295) and (18,0.183)
To find a linear expression we need the value of the slope, m.
m=(Δy-axis)/(Δx-axis)
given our points:
m=(0.183-0.295)/(18-0)=-0.112/18=-0.0062
the linear expression will be found using the formula:
m(x-x1)=(y-y1)
m=-0.0062
x1=0.295
y1=0
hence:
-0.0062(x-0)=y-0.295
-0.0062x=y-0.295
thus;
y=-0.0062x+0.295
the equation modeling the number of dropouts will be y=-0.0062x+0.295