10+9 (because first down starts at 10 yards, add 9 therefore at 19) 19+4 (add for to previous answer) 23-5 (23 subtracted by five because they gained 5 yards so it will be opposite to adding when losing yards) 18 yards is how much they need to gain to get 10 yards past the first down at 10 yards. hope I helped (:
