You can tell if a table is linear by looking at how X and Y change. If, as X increases by 1, Y increases by a constant rate, then a table is linear. You can find the constant rate by finding the first difference.
The equation can be rewritten as: Log(x*(x+5))=Log=(6x+12) so x(x+5)=6x+12 x^2+5x=6x+12 x^2-x-12=0 (x+3)(x-4)=0 x=-3 or x=4 x cannot be negative here, so x=4 is the only solution