Howi usually runs 75 miles each month.
Last month he ran an extra 16 miles. How many miles did he run last month?
Howi usually runs 75 miles each month, so he ran a total of 75 miles last month.
With the extra 16 miles, he ran a total of 75 + 16 = <<75+16=91>>91 miles last month. Answer: \boxed{91}.