First, rewrite the expression as:
#(50w)/(90 + w) = 20#
Next, multiply each side of the equation by #color(red)((90 + w))# to eliminate the fraction while keeping the equation balanced:
#color(red)((90 + w)) xx (50w)/(90 + w) = color(red)((90 + w)) xx 20#
#cancel(color(red)((90 + w))) xx (50w)/color(red)(cancel(color(black)(90 + w))) = color(red)(90 xx 20) + (w xx 20)#
#50w = 1800 + 20w#
Then, subtract #color(red)(20w)# from each side of the equation to isolate the #w# term while keeping the equation balanced:
#50w - color(red)(20w) = 1800 + 20w - color(red)(20w)#
#(50 - color(red)(20))w = 1800 + 0#
#30w = 1800#
Now, divide each side of the equation by #color(red)(30)# to solve for #w# while keeping the equation balanced:
#(30w)/color(red)(30) = 1800/color(red)(30)#
#(color(red)(cancel(color(black)(30)))w)/cancel(color(red)(30)) = 60#
#w = 60#