Question 610683
Each play that the team gains yards can be modeled as a positive value and each play that the team loses yards can be modeled as a negative value. So this problem is simply asking for the summation of the three numbers: 5, -17, and 21.

So the answer is then:
{{{ 5 - 17 + 21 }}}

Which evaluates to the net yardage of 9.