Answer:
-298.
Explanation:
This is an arithmetic sequence with first term a1 = 88 and common difference d = -13.
Sum on n terms = n/2 [2a1 + d(n - 1)]
---> sum of 15 terms = 15/2(2*88 - 13(15-1]
= 7.5 * -6
= -45
Sum of 11 terms = 11/2(2*88 - 13(11-1]
= 46*5.5
= 253
So partial sum of terms 12 to 15
= -45 - 253
= -298.