Find the coefficients of \(x ^ { 3 }\) and \(x ^ { 4 }\) in the expansion of \(( 3 - a x ) ^ { 5 }\), where \(a\) is a constant. Give your answers in terms of \(a\).
Given that the coefficient of \(x ^ { 4 }\) in the expansion of \(( a x + 7 ) ( 3 - a x ) ^ { 5 }\) is 240 , find the positive value of \(a\).
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