Let f: R - -1,4 arrow R - α, β be a function given by f ( x )=( x 2+ bx + c / x 2-3 x -4). If number of ordered pairs ( b, c), where b, c ∈ -5,-4,-3, ldots ldots 3,4,5 for which f(x) is injective is n, then ind the value of (n-7).