Question 1199392
<pre>
Maybe you're supposed to do it this way:

{{{a[n]=a[1]+(n-1)d}}}


{{{system(a[13]=a[1]+(13-1)d, a[25]=a[1]+(25-1)d)}}}

{{{system(189=a[1]+12d, 225=a[1]+24d)}}}

Solve that by substitution or elimination, then substitute
the values you get for a<sub>1</sub> and d and n=55 in

{{{a[n]=a[1]+(n-1)d}}}

Edwin</pre>