2 times the sum of 7 times a number and 4

2 times the sum of 7 times a number and 4

This is an algebraic expression. Let's take it in 4 parts:

1. The phrase a number means an arbitrary variable, let's call it x.
2. 7 times a number means we multiply x by 7: 7x
3. The sum of 7 times a number and 4 means we add 4 to 7x: 7x + 4
4. Finally, we multiply the sum in #3 by 2

Build our final algebraic expression:
2(7x + 4)