Final answer:
The equation that models the situation is x^2 - 11x + 28 = 0. The width of the frame is approximately 4 cm.
Step-by-step explanation:
The equation that models the situation described is: x^2 - 11x + 28 = 0. To find the width of the frame, we need to solve this equation. By factoring or using the quadratic formula, we find the solutions to be x = 4 and x = 7. Since the width of the frame cannot be negative, the width of the frame is approximately 4 cm.