Average cost AC = c/q = q-2+500/q.

Marginal average cost MAC = DAC/dq = 1-500/q 2.

When Q=50,

Marginal cost MC=2Q-2=98

Average cost AC=C/Q=Q-2+500/Q=58.

The marginal average cost MAC = DAC/dq =1-500/Q2 =-1.