Question

Question in attachment

Answer 1

`a_(1)=6`

Explanation:

It is sum of arithmetic progression

`$S_(20)=(20)/(2) [2a_(1)+(20-1)\cdot 4]$`

`$880=10[2a_(1)+(19)\cdot 4]$`

`$880=10[2a_(1)+76]$`

`880=20a_(1)+760`

`120=20a_(1)`

`a_(1)=6`