1. **State the problem:** We have a pentagon with interior angles 120°, 100°, 100°, 110°, and an unknown angle $f$. We need to find the value of $f$. 2. **Formula for sum of interior angles of a polygon:** The sum of interior angles of an $n$-sided polygon is given by: $$\text{Sum} = (n-2) \times 180^\circ$$ For a pentagon, $n=5$, so: $$\text{Sum} = (5-2) \times 180^\circ = 3 \times 180^\circ = 540^\circ$$ 3. **Set up the equation:** The sum of all interior angles must be 540°: $$120^\circ + 100^\circ + 100^\circ + 110^\circ + f = 540^\circ$$ 4. **Calculate the sum of known angles:** $$120 + 100 + 100 + 110 = 430$$ 5. **Solve for $f$:** $$f = 540 - 430$$ $$f = 110^\circ$$ **Final answer:** $$f = 110^\circ$$