问题
单项选择题
A laborer is paid $8 per hour for an 8-hour day and 
times that rate for each hour in excess of 8 hours in a singe day. If the laborer received $ 80 for a single day’s work, how long did he work on that day ？（）
A.6hr. 40min.
B.9hr. 20min.
C.9hr. 30min.
D.9hr. 40Min.
E.10hr.
答案
参考答案：B