For all numbers x and y the definition of the operation is x y=xy(x

For all numbers \(x\) and \(y\) the definition of the operation \(\) is \(x y=xy(x+4)\). If \((-6) a = -60,\) then what is the value of \(a\) ? A. -20 B. -5 C. 2.5 D. 5 E. 10