Answer:
Option b is correct 175
Step-by-step explanation:
n = 7
k = 6
3k -2 ------1
put k = 6 in above eq. for finding first term
a1 = 3(6) - 2 = 18 - 2 = 16
put k = 7 in above eq. for finding first term
a2 = 3(7) - 2 = 21 - 2 = 19
a3 = 3 (8) - 2 = 24 - 2 = 22
16, 19 , 22, ... //Arithmetic series formation
a1 = 16 , a2 = 19
d = a2 - a1 = 19 - 16 = 3 //Difference of first two terms
Using sum forumula for arithmetic series
sum = [tex]\frac{n}{2}(2a1 + (n-1)d)[/tex]
= [tex]\frac{7}{2}(2a1 + (7-1)d)[/tex]
= [tex]\frac{7}{2}(2(16) + (6)3)[/tex]
= [tex]\frac{7}{2}(32 + 18)[/tex]
= [tex]\frac{7}{2}(50)[/tex]
= 7 * 25
= 175
