Can someone please help me work out these problems?!!! I'm not looking for someone to give me the answers, I just need help working them out because theres something I'm not doing right.

1.)Your gross pay is $2,759.00. Your involuntary deductions are FICA (7.65%), federal withholding (12%), and state withholding (7%). How much are you allowed for housing and fixed expenses?
$772.52
$993.24
$728.54
$566.64

2.)Your mortgage is $135,400.00 at a 5.25% APR. If you pay $1,500.00 towards the mortgage each month, how much of your second month's payment is applied to the principal?
$1,815.

Question

Can someone please help me work out these problems?!!! I'm not looking for someone to give me the answers, I just need help working them out because theres something I'm not doing right.

1.)Your gross pay is $2,759.00. Your involuntary deductions are FICA (7.65%), federal withholding (12%), and state withholding (7%). How much are you allowed for housing and fixed expenses? 
$772.52
$993.24
$728.54
$566.64

2.)Your mortgage is $135,400.00 at a 5.25% APR. If you pay $1,500.00 towards the mortgage each month, how much of your second month's payment is applied to the principal? 
$1,815.