book Maths Puzzle Numerical Ability

I'm not understanding the elimination technique that my teacher is explaining. My problem is:
3x+3y-2z=-32
x-3y+z=11
-x-3y+3z=23

I don't understand how to substitute after

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book Other Question

this is for quadratic formula and parabolas which could be the graph of the parabola a.y=x2=1,b.y=x2-1,c.y=-x2=1,d=-x2-1 CD rollover. Ronnie invested P dollars in a 2-year CD with an annual rate of return of r. After the CD rolled over three times, its value was P((1 + r y^2)^3. Which law of exponents can be used to simplify the expression? Simplify it.