Bill and Mary plan to marry in December 2015. Bill’s salary is $32,000 and he owns his residence. His itemized deductions total $12,000. Mary’s salary is $39,000. Her itemized deductions total only $1,600 as she does not own her residence. For purposes of this problem, assume 2016 tax rates, exemptions, and standard deductions are the same as 2015. 
a. What will their tax be if they marry before year-end and file a joint return?
b. What will their combined taxes be for the year if they delay the marriage until 2016?
c. What factors contribute to the difference in taxes?