A nurse measured the blood pressure of each person who visited her clinic. Following is a relative frequency histogram for the systolic blood pressure readings for those people aged between 25 and 40. Use the histogram to answer the question. The blood pressure readings were rounded to the next higher whole number.
Given that 800 people were aged between 25 and 40, approximately how many had a systolic blood pressure reading greater than 140 and less than or equal to 150?
a. 8
b. 6
c. 64
d. 640