#### Answer

d)

#### Work Step by Step

If we want to write the expression in another form:
$5+10+15+20=5(1)+5(2)+5(3)+5(4)=\sum_{k=1}^45k$
The answer is d)

Published by
Pearson

ISBN 10:
0-32184-874-8

ISBN 13:
978-0-32184-874-1

d)

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