\text { Let } f(x)=\frac{a x^{2}+b x+6}{x^{2}-1} \text { where } a \text { and } b \text { are constants. } (a) If f(x) has a horizontal asymptote at y = 1, what is the value of a? (b) Given the value of a found in part (a), find b such that f(x) does not have a vertical asymptote at x = -1.