Ken is working this summer as part of a crew on a farm. He earned $8 per hour for the first 10 hours he
worked this week. Because of his performance, his
crew leader raised his salary to $10 per hour for the
rest of the week. Ken saves 90% of his earnings from
each week. What is the least number of hours he
must work the rest of the week to save at least $270 for the week? Please show how you got your answer