Question

question in attachment

Answer 1

Answer:

$a_{1}=6$

Step-by-step explanation:

It is sum of arithmetic progression

$S_{20}=\frac{20}{2} [2a_{1}+(20-1)\cdot 4]$

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

$880=10[2a_{1}+76]$

$880=20a_{1}+760$

$120=20a_{1}$

$a_{1}=6$