The correct answer is C. 7 minutes . The CSSBB material defines takt time as the available production time divided by the rate of customer demand and also gives the formula as net operating time per period / customer requirements per period . Here, the available work time is the 8-hour day minus 1 hour for meetings and breaks, leaving 7 hours of net operating time. Converting to minutes gives 420 minutes per day . The customer requires 60 invoices per day , so:

Takt time = 420 / 60 = 7 minutes per invoice

That matches option C . The listed “total work time per invoice = 5 minutes” is useful for comparing actual process cycle time to takt time, but it is not used to calculate takt time itself. In Lean Six Sigma, takt time reflects the pace required to meet demand , not the actual current processing time. Since the process must complete one invoice every 7 minutes to satisfy customer demand, the verified answer is 7 minutes per invoice .