Answer : 3. "n = 29/5"
Explanation :

Answer: C) n = 29/5 Explanation: Given are the two AP'S: 15,12,9.... in which a=15, d=-3.............(1)  -15,-13,-11..... in which a'=-15 ,d'=2.....(2)   now using the nth term's formula,we get a+(n-1)d = a'+(n-1)d' substituting the value obtained in eq. 1 and 2, 15+(n-1) x (-3) = -15+(n-1) x 2 => 15 - 3n + 3 = -15 + 2n - 2 => 12 - 3n = -17 + 2n => 12+17 = 2n+3n => 29=5n => n= 29/5