A composite rod is made by attaching a glass-reinforced plastic rod and a nylon rod end to end, as shown.
The rods have the same cross-sectional area and each rod is 
in length. The Young modulus 
of the plastic is 
and the Young modulus 
of the nylon is 
. The composite rod will break when its total extension reaches 
. What is the greatest tensile stress that can be applied to the composite rod before it breaks?
