Firstly, a X% tax cut means a X% reduction in amount of tax paid, not a X% increase in after-tax income. So $10,322 -> $9000 would be a 12.8% tax cut.

Secondly, you're forgetting standard deductions. It's $12,600 today; the Trump plan is to raise it to $30,000. So it would actually be:

$36,000 Current: $2,582 (7.2%) Trump: $720 (2.1%) $75,000 Current: $8,433 (11.2%) Trump: $4,200 (5.6%) etc…

(I hate the guy and don't think this tax plan is a terribly great idea, but the math above is wrong)