The First National Bank received 3,000 inquiries following the latest advertisement describing its 30-month IRA accounts in theBoston World, a local newspaper.The most recent ad in a similar advertising campaign inMassachusetts Business, a regional business magazine, generated 1,000 inquiries.Each newspaper ad costs $500, whereas each magazine ad costs $125.

b. Holding all else equal, how many inquiries must a newspaper ad attract for the current advertising mix to be optimal.