What would have to be true about the taxable income of an Australian for her marginal and average tax rates to be the same?

Taxable income Tax on this income 0 - $18,200 Nil $18,201 - $37,000 19c for each $1 over $18,200 $37,001 - $90,000 $3,572 plus 32.5c for each $1 over $37,000 $90,001 - $180,000 $20,797 plus 37c for each $1 over $90,000 $180,001 and over $54,097 plus 45c for each $1 over $180,000 Taxable income Tax on this income 0 - $18,200 Nil $18,201 - $37,000 19c for each $1 over $18,200 $37,001 - $90,000 $3,572 plus 32.5c for each $1 over $37,000 $90,001 - $180,000 $20,797 plus 37c for each $1 over $90,000 $180,001 and over $54,097 plus 45c for each $1 over $180,000