{2}(-7{n}b{n})*{3}(-ab)-[5a{2n}*{3}(-a)*b{2n}*{3}b]
=4(-7{{n}}b)*(-9ab)-[10an*(-9a)*4b{n}*9b]
=252a{b}{{n}}-(-3240{a}{b}{n})
=252a{b}{{n}}+3240{a}{b}{n}