<PRE><B>Question 1209780</B>
&lt;br&gt;
21+27+33+...+6021&lt;br&gt;
The common difference is 6, so the formula for the n-th term is of the form&lt;br&gt;
t(n) = 6n+b&lt;br&gt;
t(1) = 21, so the formula is&lt;br&gt;
t(n) = 6n+15&lt;br&gt;
The last term is 6021:&lt;br&gt;
6n+15 = 6021
6n = 6006
n = 1001&lt;br&gt;
The sequence is 1001 terms with first term 21 and last term 6021.&lt;br&gt;
Sum = (number of terms) * (average of all the terms) = (number of terms) * (average of first and last terms)&lt;br&gt;
{{{(1001)((21+6021)/2)=(1001)(3021)=3021000+3021=3024021}}}&lt;br&gt;
ANSWER: 3024021&lt;br&gt;
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