Schedule 1-A is the IRS form that is used to calculate the Enhanced Deduction for Seniors in Part V. The form is here: Schedule 1-A.
Line 31 of the form uses your income - in your case $180,000
Line 32 is the beginning of the phaseout range - for you $150,000
Line 33 is line 32 minus line 31 or $30,000
Line 34 you multiply line 33 by 0.06 which is $1800
Line 35 you subtract line 34 from $6,000 to get $4,200
Line 36a is line 35 if you are 65 or older - or $4,200
Line 36b is 0 if you are single or is the same as line 36a if you are married filing jointly and your spouse has a valid SSN - in your case this would also be $4,200
Your enhanced deduction for seniors is the sum of line 36a and 36 which would be $8,400
So if your senior deduction is calculated at $8,400 for an income of $180,000, then it is correct.
