Respuesta :

The 1st, 4th, and 7th terms make an arithmetic sequence of their own. The 4th term is the average of the 1st and 7th, so ...
   (1st +7th)/2 = 4th
   1st + 7th = 2×4th
   1st = 2×4th - 7th

The first term is ...
   2*141 - 132 = 150