book Maths Puzzle Numerical Ability

How do I work out these problems 1x+1y=2 , -5x+1y=20 and -5/-7x+ 1y=-10/-7
to get these answers (-3,5), (-5,-5), and (2,0)?

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book Other Question

I have a few problems like this one on my assignment and can't figure them out. I am familiar with the formula r = d/t, but I don't know how to use it in these situations:

"Naok what is a expression