Answer
$x = 496.5$
Work Step by Step
$\log (2x+7) = 3$
$\log_{10} (2x+7) = 3$
$10^{3} = 2x + 7$
$1000 = 2x + 7$
$1000 - 7 = 2x$
$993 = 2x$
$x = 496.5$
Check:
$\log_{10} (2(496.5)+7) \overset{?}{=} 3$
$\log_{10} (993+7) \overset{?}{=} 3$
$\log_{10} (1000) \overset{?}{=} 3$
$\log_{10} (10^{3}) \overset{?}{=} 3$
$3 = 3$