For this type of problems we recall the definition of the complementary number of another number:
Let's say we have a number x, then the complementary number of x is a number for which the following happens:

Where n is the minimum number such that

For example: the complementary number of 5 is 5, the complementary number of 100 is 0, the complementary number of 350 is 650.
Answer: the complementary number of 54 is 100-54= 46.