I have a question which is Find the constant k such that the following is a valid pmf

$\displaystyle p_0 = 5k, p_1 = 4k, p_2 = 3k, p_3 = 2k$

tbh i dont even know what the p values are would they be the probabilities or the masses? and then i still dont know how to do it as thats the only info your given