Determine whether each of the following congruences has a solution: (All of the moduli are primes.) continued.?

QUESTION CONTINUED: (a) x^2 congruent to -1(mod 5987) ; (b) x^2 congruent to 6780(mod 6781) ; (c) x^2 + 14x -35 congruent to 0(mod 337); and (d) x^2 - 64x + 943 congruent to 0(mod 3011).