Answer
$x = 0.20$
Work Step by Step
$\log (x+7) - \log 3 = \log (7x+1)$
$\log \frac{x+7}{3} = \log (7x+1)$
$\log \frac{x+7}{3} - \log (7x+1) = 0$
$\log \frac{x+7}{3(7x+1)} = 0$
$\log \frac{x+7}{21x+3} = 0$
$1 = \frac{x+7}{21x+3}$
$\frac{x+7}{21x+3} = 1$
$x+7 = 1(21x + 3)$
$x+ 7 = 21x + 3$
$x - 21x = - 7 + 3$
$-20x = -4$
$x = \frac{4}{20}$
$x = \frac{1}{5}$
by GDC / calculator
$x = 0.20$
