1. **State the problem:** Alexander initially has 15 birds, 7 of which are pink. He buys 6 more pink birds. We need to find the fraction of pink birds out of the total birds now. 2. **Calculate the new number of pink birds:** $$7 + 6 = 13$$ 3. **Calculate the new total number of birds:** $$15 + 6 = 21$$ 4. **Find the fraction of pink birds:** $$\frac{13}{21}$$ 5. **Simplify the fraction if possible:** 13 and 21 have no common factors other than 1, so the fraction is already in simplest form. **Final answer:** The fraction of Alexander's birds that are pink now is $$\frac{13}{21}$$.