Which shows another way to write 64?

a.
6 x 6 x 6 x 6

b.
6 x 4

c.
4 x 4 x 4 x 4 x 4 x 4

d.
6 + 6 + 6 + 6

i want to say a but i feel i maybe wrong.

Nick and nora are married and have three children in college. they have an adjusted gross income of 47,400. if their standard deduction is 12,600 itemized deductions are 14,200 and they get an exemption of 4000 for each adult and each dependent what is their taxable income