DISCUSSION THREAD
Hints: Consider using the method of joints starting with joint C, followed by joint D. This will provide the needed equations to solve for the loads carried by the four members in the truss.
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For this problem, will we need to utilize the given value for Poisson's ratio to solve in part b and c? Since we solve for the stress in part a and we are given the value for Young's modulus, can we use the relation that E = stress/strain and from there solve for the elongation of DH?
As a general statement, material properties and geometric dimensions are often provided without regard as to whether all of those parameters will be needed to arrive at the answer.
For this particular problem, your approach looks good.