Answer :
[tex] s_{n}=n( \frac{ a_{1} + a_{n} }{2} )[/tex]
[tex] s_{n}=4( \frac{ (395(1)+4519)+(395(4)+4519)}{2}) [/tex]
[tex] s_{n} =4( \frac{5814+6999}{2}) [/tex]
[tex] s_{n}=4( \frac{12813}{2}) [/tex]
[tex] s_{n}=4(6406.5) [/tex]
[tex] s_{n}=25626 [/tex]
[tex] s_{n}=4( \frac{ (395(1)+4519)+(395(4)+4519)}{2}) [/tex]
[tex] s_{n} =4( \frac{5814+6999}{2}) [/tex]
[tex] s_{n}=4( \frac{12813}{2}) [/tex]
[tex] s_{n}=4(6406.5) [/tex]
[tex] s_{n}=25626 [/tex]