The daily revenue from the sale of fried dough at a local street vendor in Boston is known to be normally distributed with a known standard deviation of $120. The revenue on each of the last 25 days is noted, and the average is computed as $550. Construct a 90% confidence interval for the population mean of the sale of fried dough by this vendor.

a. 550 1.96(120/5)

b. 120 1.96(550/5)

c. 550 1.645(120/5)

d. 120 1.645(550/5)