Finding the First Term and Common Difference of an Arithmetic Series

[Blister]

Homework Statement

The sum of the first 4 terms in an arithmetic series is -8 and the sum of the first 5 terms is 85. Determine the first term and the common difference.

Homework Equations

tn = a + (n-1)d
Sn = n/2 (2a + (n-1)d)

The Attempt at a Solution

 

[rock.freak667]

The Attempt at a Solution

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