1. **State the problem:** Calculate the perimeter of an L-shaped composite figure with sides 4 ft, 7 ft, 3 ft, 5 ft, and 12 ft. 2. **Formula:** The perimeter of a polygon is the sum of the lengths of all its sides. 3. **Important rule:** For composite figures, add all outer side lengths without double counting any side. 4. **Identify all sides:** The figure has sides 4 ft (top), 7 ft (right upper), 5 ft (right lower), 3 ft (bottom), and 12 ft (left). 5. **Calculate perimeter:** $$\text{Perimeter} = 4 + 7 + 5 + 3 + 12$$ 6. **Simplify:** $$4 + 7 = 11$$ $$11 + 5 = 16$$ $$16 + 3 = 19$$ $$19 + 12 = 31$$ 7. **Final answer:** $$\boxed{31\text{ ft}}$$ The perimeter of the L-shaped figure is 31 ft.