10(g + 5) = 2(g + 9)....distribute thru the parenthesis
10g + 50 = 2g + 18...subtract 2g from both sides
10g - 2g + 50 = 2g - 2g + 18....simplify
8g + 50 = 18....subtract 50 from both sides
8g + 50 - 50 = 18 - 50...simplify
8g = - 32...divide both sides by 8....cancelling the 8 on the left side
g = -32/8
g = -4