Question 974658
<pre>
Memorize the formula

{{{a[n]}}}{{{""=""}}}{{{a[1]r^(n-1)}}}

Plug in and simplify: 

{{{a[6]}}}{{{""=""}}}{{{20(-3)^(6-1)}}}

{{{a[6]}}}{{{""=""}}}{{{20(-3)^5}}}

{{{a[6]}}}{{{""=""}}}{{{20(-243)}}}

{{{a[6]}}}{{{""=""}}}{{{-4860}}}

Edwin</pre>