book Maths Puzzle Numerical Ability

I am not certain of the steps for this;
ar^2 - brs + ars - br^2 = ar^2 + ars - brs - br^2

Thanks,
ttsj

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book Other Question

This question is actually about elimination because there werent any catorgories for elimination. My question is:
0.5x+0.5y=-2
x-0.25y=6

My answer was (2.5,-14) but I don't th find the equation of the line perpendicular to line "b" and passing throught the point (4, -7).