Key idea. Group terms to create a repeated bracket.

1. Group the first two terms and the last two:

   \[(ab+ac)+(bd+cd).\]

2. Take out the common factor in each group:

   \[a(b+c)+d(b+c).\]

3. The whole bracket \(b+c\) is now a common factor, giving \((a+d)(b+c)\).

Remember. Grouping works when it produces the same bracket more than once.