Use the values of a_1( 1 is below the a) and s_n (n is below also) to find the value of a_23. A_1=10, s_23=2760, find the value of a_23

Please help, I really need help. Thanks.

[(a1 + a23)/2] * 23 = s23

[(10 + a23) / 2] * 23 = 2760