Question 1085514
{{{a[n]=a[1]+(n-1)*d}}}
So,
{{{a[8]=a[1]+(8-1)*d=54}}}
1.{{{a[1]+7d=54}}}
and
{{{a[9]=a[1]+(9-1)*d=60}}}
2.{{{a[1]+8d=60}}}
Subtracting 1 from 2,
{{{a[1]+8d-a[1]-7d=60-54}}}
{{{d=6}}}
So then,
{{{a[1]+7(6)=54}}}
{{{a[1]+42=54}}}
Now solve for {{{a[1]}}}.