First, expand the terms in parenthesis by multiplying each term within the parenthesis by the term outside the parenthesis:
#color(red)(2)(42 - 2x) + color(blue)(2)(25 - 2x) = 500#
#(color(red)(2) xx 42) - (color(red)(2) xx 2x) + (color(blue)(2) xx 25) - (color(blue)(2) xx 2x) = 500#
#84 - 4x + 50 - 4x = 500#
Next, group and combine like terms on the left side of the equation:
#84 + 50 - 4x - 4x = 500#
#(84 + 50) + (-4 - 4)x = 500#
#134 + (-8)x = 500#
#134 - 8x = 500#
Then, subtract #color(red)(134)# from each side of the equation to isolate the #x# term while keeping the equation balanced:
#-color(red)(134) + 134 - 8x = -color(red)(134) + 500#
#0 - 8x = 366#
#-8x = 366#
Now, divide each side of the equation by #color(red)(-8)# to solve for #x# while keeping the equation balanced:
#(-8x)/color(red)(-8) = 366/color(red)(-8)#
#(color(red)(cancel(color(black)(-8)))x)/cancel(color(red)(-8)) = -45.75#
#x = -45.75#