To qualify for this Challenge Cache, either the sum or the product of the difficulty and terrain for every square of your difficulty/terrain grid, multiplied by the number of finds, should equal 50 or more.
For example, you have 4 finds at difficulty 3.5, terrain 4. (3.5 + 4) * 4 = 30 which does not qualify, but (3.5 * 4) * 4 = 56 which does.
Here is a table showing how many finds you need in each square:
See the cache page for Bronze for parking.