Question 309124
Here's what you know,
{{{a(12)=5}}}
{{{d=-2}}}
Here's the general equation. 
{{{a(n)=a1+(n-1)*d}}}
Plug in what you know,
{{{a(12)=a1+(12-1)*(-2)=5}}}
Now solve for {{{a1}}}
{{{a1+11(-2)=5}}}
{{{a1-22=5}}}
{{{a1=27}}}