33+(n- 12)* 1 1/3 = 263，n = 230 * 3/ 1 1- 12

2. solution: a9-a5=4d, 60- 12=4d, d= 12, a1= a5-4d =12-48 =-36, a12.

an = a 1+(n- 1)d =-36+ 12(n- 1)