Explanation
The hourly error rate for this machine is the error rate in parts per 100 multiplied by the number of parts produced per hour: \(\frac{4}{100} \times 8=0.32\) errors per hour
So, in an average hour, the machine will produce 8 - 0.32 = 7.68 error free parts.
The machine ran for 24 - 8 = 16 hours yesterday so you would expect that \(16 \times 7.68 = 122.88\) approximately 122.9 error free parts were produced yesterday.