[tex]( {3}^{21} - {3}^{20} - {3}^{19} ) \div ( {9}^{8} \times 5)[/tex]
[tex]=[ {3}^{19}( {3}^{2} - 3 - 1) ] \div [ {( {3}^{2} )}^{8} \times 5 ][/tex]
[tex] = [ {3}^{19} (9 - 3 - 1)] \div ( {3}^{2 \times 8} \times 5)[/tex]
[tex] = ( {3}^{19} \times 5) \div ( {3}^{16} \times 5)[/tex]
[tex] = ( {3}^{19} \div {3}^{16}) \times( 5 \div 5)[/tex]
[tex] = {3}^{19 - 16} \times 1[/tex]
[tex] = {3}^{3} \times 1[/tex]
[tex] = {3}^{3} [/tex]
[tex] = 27[/tex]
