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