Question 1036199
From the given, {{{a[10] - a[7] = -60}}} and {{{a[12]/a[6] = 2}}}.

The first equation becomes {{{a[1] +9d - (a[1]+6d) = -60}}} ==> 3d = -60 ==> d = -20.

The second equation becomes {{{a[12] = 2a[6]}}}.

==> {{{a[1] + 11*-20 = 2(a[1] + 5*-20)}}}

<==> {{{a[1] - 220 = 2a[1] - 200}}}

==> {{{a[1] = -20}}}