Please check if my answers are correct, if not, please help me by correcting them! Thanks in advance.

Here's what I think...Find all real numbers, x, that satisfy $\displaystyle 6^x 7^{2x} = 86,436$

$\displaystyle 42^{2x^{2}} = 86,436$

$\displaystyle 2x^2 = 2,058$

$\displaystyle 2x = +/- \sqrt {45.365}$

$\displaystyle x = +/- 22.68$

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I think there will be 27 billion sold because of $\displaystyle 3^{3}$ since 9 billion in 2000 is $\displaystyle 3^{2}$ ...The total number of hamburgers sold by a national fast-food is growing exponentially. If 3 billion had been sold by 1995 and 9 billion had been sold by 2000, how many will have been sold by 2005?