7. (3 points) A deck of playing cards has 54 cards. How many cards must be drawn to ensure that: there are cards of all four suits.

At least $\qquad$ cards must be drawn to ensure that there are cards of all four suits.
7. (3 points) A deck of playing cards has 54 cards. How many: at least _42_ cards must be drawn to ensure that all four suits are present.
【Solution】According to the analysis, we get,
$$
13 \times 3+2+1=42 \text { (cards), }
$$

Answer: At least 42 cards must be drawn to ensure that all four suits are present.
Therefore, the answer is: 42.