Question 892169
General term of the sequence, {{{a+(n-1)d}}};
a = first term
n = index of the term
d = common difference


Your final term used in the series is n=4 for the expression {{{a+3d}}}.

The term at n=2 is {{{a+d=7}}}.


The sum of your first four terms is {{{(4/2)(firstTerm+lastTerm)}}},
{{{(2)(a+a+3d)=12}}}
{{{(2)(2a+3d)=12}}}
{{{2a+3d=6}}}


Solve the system
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{{{system(a+d=7, 2a+3d=6)}}}
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