Edexcel C1 problem - AP's

[Zorber]

The 5th term of an arithmetic series is 14 and the sum of the first three terms of the series is -3.
Use algebra to show that the first term of the series is -6 and calculate the common difference of the series.

[KatieB]

given 5th term = 14
=> a+4d=14 (1)
Also since Sum of the first 3 terms = -3
=> a+(a+d)+(a+2d) = -3
=> 3a+3d=-3
divide by 3
=> a+d = -1 (2)
(1)-(2) gives
=> 3d=15
=> d=5

Sub d=5 into (2)
=> a+5=-1
=> a=-6