The triangle inequality tells you the third side will be between the difference and sum of the other two sides.
5 < third side < 21
4(3+x)
This is because 4*3=12 and 4*x is 4x so you get 12+4x which is the original equation
Americans work an average of 34.4 hours per week. The average hours per week worked varies based on gender, marital status, and race.
