Solving linear equations is not for me : b i need to know
p - 15 = 13 - 6p

First of all, let's make sure we know what a 'solution' is, so that when you
have it, you'll know it.

The 'solution' is a NUMBER.  It's the number that  'p'  must be, in order to
make the equation a true statement.  There's only one of them.

p - 15 = 13 - 6p

Add  6p  to each side:        7p - 15 = 13

Add  15  to each side:        7p        = 28

Divide each side by  7 :        p        = 4

Was that so tough ?