book Maths Puzzle Numerical Ability

i just dont understand how to do these problems
OR how to FOIL
someone help me!!!!

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book Other Question

twenty-minus a number is 42.find the number 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