Final answer:
To find the maximum length of a side of a rectangle with a perimeter of 90, it must be less than half the perimeter. The only choice provided that is less than 45 is 20 meters.
Step-by-step explanation:
The student has asked the length of the longest side of a rectangle when the perimeter is 90 meters. To solve this, we use the formula for the perimeter of a rectangle, which is P = 2l + 2w (where P is the perimeter, l is the length, and w is the width). Since a rectangle has two pairs of equal sides, the longest side cannot be more than half of the perimeter. Therefore, the longest side must be less than 45 meters. Looking at the answer choices, the only option less than 45 meters is option B) 20 meters.