If first and last term of an AP are $a$ & $l$ and sum of all terms is $s$, then common difference is

Question

$(a)\;\frac{l^2+a^2}{s-(l-a)}\qquad(b)\;\frac{l^2+a^2}{2s-(l+a)}\qquad(c)\;\frac{l^2-a^2}{s-(l+a)}\qquad(d)\;\frac{l^2-a^2}{2s-(l+a)}$