book Maths Puzzle Numerical Ability

how do u do this 2x+3y=(-4)
x+y=(-2)

and this x+2y=0
y=3

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Can you please help me with this problem: Find each value given that f(x)=2x+1
f(3)+f(2).
And: Find the domain and range of f(x)= 1/x-4. I know the domain is x and the range is y, but how do I figure it on a fraction?
Thank You can i have the formula of this "area of a trapezoid given its baes1,base2 ane height"