Drawing balls without replacement

A bag contains balls numbered with integers from \(1\) to \(7\) (inclusive). Two balls are drawn from the bag without replacement, having values \(x,y.\) The expected value of \(xy\) can be expressed as \(\frac{a}{b}\) where \(a\) and \(b\) are coprime positive integers. What is the value of \(a + b?\)

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