Lennalyn,
We first need to find out the total number of possible cards.
There are 4 Jacks in a 52 card deck
There are 13 spades in a 52 card deck
There is a total of 16 possible cards (13 + 4 -1 = 16). - the reason why I subtracted 1 is because the Jack of spades is both a Jack and also a spade. When counting the number of jacks and the number of spades, the jack of spades got counted twice.
Answer: 16/52 = 0.31(rounded 2 decimal places) = 31%