**A can do a certain work in 15 days, while B can do the same work in 21 days. If they work together, then in how many days will the same work be completed?** A) $$ 6\\frac{3}{4} $$ B) $$ 9\\frac{3}{4} $$ C) $$ 7\\frac{3}{4} $$ D) $$ 8\\frac{3}{4} $$ Click Link for Answer