1. **State the problem:** Given an angle measuring 20°, find the measure of its complementary angle. 2. **Recall the definition:** Complementary angles are two angles whose measures add up to 90°. 3. **Set up the equation:** Let the complementary angle be $x$. Then, $$20 + x = 90$$ 4. **Solve for $x$:** $$x = 90 - 20$$ $$x = 70$$ 5. **Interpretation:** The complementary angle to 20° is 70° because together they sum to 90°. **Final answer:** The measure of the complementary angle is **70°**.