book Maths Puzzle Numerical Ability

y=4x+1
y=4x-3

i am trying to solve this by elimination, substitution or graphing. i think that if a mult. the 2nd equation by -1, i can use elimination. however, it will cancel

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book Other Question

How many gallons of a 15% acid solution must be mixed with 2 gallons of a 23% acid solution to make a 18% acid solution? I do not understand.

x+2 over x over x-2 over 3x

(x+2/x) / (x-2)/3x

Please help!