Okay... Let's try to understand it. 
1. We see standard elf-file. If we start it in the terminal, he ask us "What is my favourite number?". Reverse is starting...;2. You should open IDA, or other disassembler, like Ghidra or BinaryNinja;3. Decompilation show us "libcstartmain()" function that open main() function;4. Follow to main function and see our programm. It ask us its favourite number and in the next string it push our input in the variable. The variable has comparision with the number "549255";5. Now we can write it in the terminal and get our flag;
P.s. If your elf-file hasn't execution use " chmod u+x 'elf-file' " to correct it.