What are the normal strains in string AB and string BC$?$

$***$ problem $9-6$ given below for context, please do problem above$***$

The A$-36$ steel drill shaft of an oil well extends $12,000ft$ into the ground. Assuming that the pipe used to drill the well is suspended freely from the derrick at $A,$ determine the maximum average normal stress in each pipe string and the elongation of its end $D$ with respect to the fixed end at $A.$ The shaft consists of three different sizes of pipe, $AB,BC,$ and $CD,$ each having the length, weight per unit length, and cross$-$sectional area indicated.