Answer
$29.10\ mL$
Work Step by Step
Number of moles of $OH^-$:
$200.\ mg\div78.00\ mg/mmol\times3+200.\ mg\div58.32\ mg/mmol\times2=14.55\ mmol$
Same number of moles of acid to complete neutralization:
$14.55\ mmol\div0.500\ M=29.10\ mL$
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