System of Linear Equations

Hi guys, I have scanned the question as its easier than typing it out and put it online here (sorry its kinda bad quality):

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If you guys cant see the image properly then tell me and I will try and clarify the problem.

Ok so my answers for question (i) is

I3 = 1 + (19/12)A

I2 = 1 + (5/4)A

I1 = 1 + (1/4)A

Is this right?

My answer for question (ii) is

A = 12

But can somebody show me how they would show that A = 12, if that is actually the right answer, and if not what is the right answer and how to get to it.

Thanks in advance