A football team has a net yardage of −23 1
3
yards on a series of plays. The team needs a net yardage of 30 yards to get a first down. How many yards do they have to get on their next play to get a first down?

On their next play the team needs to get yards to get a first down.

A net yardage of -26(1/3) yards would mean that the ball is twenty six and a third yards behind where the team started the first down.  So first, the ball would have to travel the 26(1/3) yards to the original line of scrimmage plus another 10 yards to get the first down.  

26(1/3) + 10 = 36(1/3) yards.

Another way to calculate distance traveled is Distance = End Position - Beginning Position

Therefore, Distance = 10 - (-26(1/3)) = 36(1/3) yards.

Either way, same answer.