Answer
$g \approx -4.046...$
Work Step by Step
$8.4g + 7.6 = 3.2(g-4.2)$
$8.4g + 7.6 = 3.2g - 13.44$
$8.4g - 3.2g = -13.44 - 7.6$
$5.2g = -21.04$
$g = \frac{-21.04}{5.2}$
$g \approx -4.046...$
Check:
$8.4(-4.046...) + 7.6 \overset{?}{=} 3.2((-4.046...)-4.2)$
$(-33.987...) + 7.6 \overset{?}{=} 3.2(8.2461...)$
$(-26.387...) = (-26.387...) $