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:
\((\frac{6}{100}) \times 90=0.06 \times 90=5.4 \text { errors per hour }\)
So, in an average hour, the machine will produce 90 - 5.4 = 84.6 error free parts. The machine ran for 24 - 8 = 16 hours yesterday so you would expect that \(16 \times 84.6 = 1353.6\) error free parts were produced yesterday.