Using: \(S_n = \frac{n}{2} (a + l)\) where:- \(S_n\) is the sum of the first \(n\) terms, \(a\) is the first term, \(l\) is the last term. Given: \(S_n = 252\), a = -16, l = 72 Step 1: Substitute the Known Values Substituting the values into the sum formula: \(252 = \frac{n}{2} (-16 + 72)\) \(252 = \frac{n}{2} \cdot 56\) \(504 = n \cdot 56\) Now, divide both sides by 56: n = \(\frac{504}{56}\) = 9 Thus, the number of terms in the series is: 9