The rate at which a plant grows is constant. at the 3rd week it is 12 inches tall and at the 5th week it is 20 inches tall. if this information is plotted in a coordinate plane, what is the y- coordinate of the point (1,y)?

First, you want to find the slope of the line. You do this by taking the difference in the heights divided by the difference of the time.
m=(20-12)/(5-3)
m=8/2
m=4
Now plug the information into slope intercept form (you can choose whichever set of data you want, just as long as you are consistent):
y=mx+b
12=(4)(3)+b
12=12+b
b=0
This is saying that there is no y-intercept (b).
So our final equation is:
y=4x
The question is asking for y when x is 1, so just plug it into the equation:
y=4(1)
y=4

Hope this helps!