Sum of Arithmetic Progression

The given series is an Arithmetic Progression (AP) with first term $a = -64$, common difference $d = -2$, and last term $a_n = -100$. $a_n = a + (n-1)d \implies -100 = -64 + (n-1)(-2) \implies -36 = -2(n-1) \implies n = 19$ Sum $S_n = \frac{n}{2}(a + a_n) = \frac{19}{2}(-64 - 100) = 19 \times (-82) = -1558$.