You need to use the equation that relates the given members of the arithmetical series, such that:

`a_7 = a_3 + 4d`

The problem provides the members `a_7` and `a_3` , such that:

`20 = 8 + 4d => 4d = 20 - 8 => 4d = 12 => d...

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You need to use the equation that relates the given members of the arithmetical series, such that:

`a_7 = a_3 + 4d`

The problem provides the members `a_7` and `a_3` , such that:

`20 = 8 + 4d => 4d = 20 - 8 => 4d = 12 => d = 3`

You need to use the equation that relates the members `a_3` and `a_1` , such that:

`a_3 = a_1 + 2d => 8 = a_1 + 2*3 => a_1 = 8 - 6 => a_1 = 2`

**Hence, evaluating the member `a_1` and common difference `d` yields `d = 3` and **`a_1 = 2.`