The common difference is 6. Now, plug this into the equation for the sum of an arithmetic sequence: [tex] \frac{n}{2}[2a(1) + (n-1)d] [/tex] a(1) is 3 (the first number) n = 36 (the number of terms to sum up to) d = 6 (common difference) [tex]18[6 + (35*6)][/tex] [tex]18[216][/tex] 3888
