Data Sufficiency Competition--Prizes can be won

The sum of the first N-1 terms of an Arithmetic Progression is zero or positve and sum of the first N terms is negative. What is the value of N?

1. The common difference is -4 and the 7th term is the last positive term.
2. The first term is 25 and there are 7 positive terms and all are integers.

from one

if the difference is -4 and the 7th term = a-24 is the last positive

thus 24<a<28 thus a could be anything in this interval .

if a = 25 sum = 91 , a = 26 thus sum = 98 if we assumed a = 27 thus sum = 105
for the sum to be -ve the sum of terms after the last positive term (7) must be greater than , either

-91 or -98 or -105...

the sum of terms from 8 to 14 if we assumed a = 25 is 105

thus n-1 = 14 thus n= 15

the sum of terms from 8 to 14 if we assumed a = 26 is -98

thus n-1 = 14 thus n = 13
insuff

we need not to try fractions because either ways it is insuff

two...suff B is my answer