How do you solve #319= \frac { r } { 21} - - 296#?

First, rewrite the right side of the equation as (remember, minus a minus is a plus):

#319 = r/21 + 296#

Next, subtract #color(red)(296)# from each side of the equation to isolate the #r# term while keeping the equation balanced:

#319 - color(red)(296) = r/21 + 296 - color(red)(296)#

#23 = r/21 + 0#

#23 = r/21#

Now, multiply each side of the equation by #color(red)(21)# to solve for #r# while keeping the equation balanced:

#color(red)(21) xx 23 = color(red)(21) xx r/21#

#483 = cancel(color(red)(21)) xx r/color(red)(cancel(color(black)(21)))#

#483 = r#

#r = 483#