Answer:
75 ≤ length < 85
Explanation:
You know a number 5 or greater will round up to the next higher number in the number place to its left. Similarly, numbers less than 5 round down (get replaced by zero).
This means that 75 will round up to 80. and 84.9999... will round down to 80.
a) The lower bound on length is 75. The length must be at least 75.
b) The upper bound on length is 85. The length must be less than 85.