Answer
a)21
b)3500
c)2620
Work Step by Step
a)$\Sigma^7 _{k=1}$3=3(7)=21
b)$\Sigma^{500} _{k=1}$7=7(500)=3500
c)let
$j=k-2$
$k=j+2$
if $k=3 =>j=1$
and
if $ k=264 => j=262$
=a)$\Sigma^{264} _{k=3}$ 10
=a)$\Sigma^{262} _{j=1}$10=10(262)=2620