First, add #color(red)(3)# to each side of the equation to isolate the #p# term while keeping the equation balanced:

#13p^2 - 3 + color(red)(3) = 4209 + color(red)(3)#

#13p^2 - 0 = 4212#

#13p^2 = 4212#

Now, divide each side of the equation by #color(red)(13)# to isolate #p^2# while keeping the equation balanced:

#(13p^2)/color(red)(13) = 4212/color(red)(13)#

#(color(red)(cancel(color(black)(13)))p^2)/cancel(color(red)(13)) = 324#

#p^2 = 324#

Now, take the square root of each side of the equation to solve for #p#. Remember, the square root of a number produces a negative and positive result:

#sqrt(p^2) = +-sqrt(324)#

#p = +-18#