Answer:
Step-by-step explanation:
Arithmetic sequence
First term a = 13
Common difference = 2nd term - first term
= 22 - 13
d = 9
[tex]a_{n}= a + (n-1)d\\\\a_{7}= 13 + 6*9[/tex]
= 13 + 54
= 67
Sum of 7 terms = [tex]\frac{n}{2}(2a + (n-1)d)\\\\[/tex]
= [tex]\frac{7}{2}(2*13+6*9)\\[/tex]
=[tex]\frac{7}{2}(26+54)\\[/tex]
= [tex]\frac{7}{2}*80\\[/tex]
= 7 *40
= 280
