Now, and .
Since you titled this "Lagrange multipliers", I assume you know that the optimum value will be where for some number . In this case, that means so you have the two equations and . I recommend dividing one equation by another to eliminate , that you don't really care about, and then using the constraint to solve for and . Of course, you answers will be in terms of , , , , and I.
To answer the second question, subtract the result with "I" from the result with " ".