Question: Overlay two lines from different graphs

I want to exactly (well roughly speaking) overlay two lines from different graphs. 

So suppose I had two datasets, 

a:=[1.4,2.1,4.6,3.7,3,2.1,2,1,1.5]:
b:=[78,75,97,98,105,95,88,75,67]:

with(plots):

aa:=listplot(a):
bb:=listplot(b):

I want to overlay the two lines to compare them.  I transformed them into 3d then rotated to overlay but maple keeps scaling the axes to fit. 

Any ideas?

 

Please Wait...