In a US family with two adults and two children, the adults earned $70,000 and $30,000, respectively, and had no other income during 2017. They paid $6,000 mortgage interest, $5,000 local property tax, $4,000 state income tax, had $3,000 of employee expenses, and made $1,000 worth of charitable donations that year. They also deposited $2,000 in a Roth I.R.A. and paid $7,000 for child care. Under the law applying to 2017, they got a $600 child care tax credit and $2,000 child tax credit. Assume that the adults pay income tax. jointly as a married couple.

a. What is their 2017 federal income tax? Explain your steps in calculating the answer. 

b. How much federal income tax would they have owed if the 2017 TCAJ act applied to their 2017 income and expenses? Explain your steps in calculating the answer and describe which parts of the reform changed their tax liability.