Suppose that you enter into 4 short futures contracts to sell December silver for $23.29 per ounce. The size of each contract is 5,000 ounces. The initial margin is $12,500, and the maintenance margin is $8,000. (margin account is for all 4 contracts)

a. What change in the futures price will lead to a margin call?

b. Explain how margin accounts protect futures traders against the possibility of default.