Question 1085358
I'll do one, you do the next.
1.{{{a[4]=a[1]+(4-1)d=a[1]+3d=8}}}
2.{{{a[21]=a[1]+(21-1)d=a[1]+20d=26}}}
Subtracting,
{{{a[1]+20d-a[1]-3d=26-8}}}
{{{17d=18}}}
{{{d=18/17}}}
and
{{{a[1]+3(18/17)=8}}}
{{{a[1]=136/17-54/17}}}
{{{a[1]=82/17}}}
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.

So then,
{{{a[61]=82/17+(61-1)(18/17)}}}
{{{a[61]=82/17+1080/17}}}
{{{a[61]=1162/17}}}
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.
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Do the next one the same way.