The phrase "Lamar decreased his collection of cards by seven" can be expressed mathematically as:
\[ x - 7 \]
where \( x \) represents the original number of cards in Lamar's collection.
From the provided options, the one that best represents this operation (though not exactly, assuming a possible error in options) would be:
02 - 7, if we assume "02" represents the variable x (though it is unconventional to write a variable with a leading zero).
However, as none of the options perfectly match "x - 7," it's important to clarify that the correct expression for the phrase in a typical format would be \( x - 7 \). If you need to choose from the given options, please confirm what "02" represents, or if there's a specific context or notation that applies.