A rectangle with width $\frac{3}{4}$cm and area 3 $\frac{3}{8}$cm$^2$. Find the length

Analyze the question: We know the width and the area of a rectangle, and we need the length.

Concept: Area = length × width, so Length = Area ÷ Width.

Solution:

1. Convert the mixed number to an improper fraction: 3 3/8 = (3×8 + 3)/8 = 27/8

2. Divide the area by the width: Length = 27/8 ÷ 3/4

3. Dividing by a fraction means multiplying by its reciprocal: Length = 27/8 × 4/3 = 108/24

4. Simplify: 108/24 = 9/2 = 4 1/2 cm

Check: 4 1/2 × 3/4 = 9/2 × 3/4 = 27/8 = 3 3/8 cm². ✓

Answer: B (4½ cm)

Tip: For any "find the missing side" question, rearrange the formula first (Length = Area ÷ Width). Then use "keep, change, flip" for fraction division: keep the first fraction, change ÷ to ×, and flip the second fraction. Always check by multiplying back.