Read the post title

The + is overloaded, so it is no longer the mathematical + but performs a different function. Each digit on the LHS gives 2 digits on the RHS. Since, there are 6 digit answers for all the 3 cases.

For the first 2 digits :

Multiply the first digit with the sum of digits to get the first 2 digits of the answer.

For the middle 2 digits :

Notice that 28-9=19, 52-7=45, 34-6=28

For the last 2 digits :

The last two digits => reverse{(largest number)*(smallest number) – (remaining number)}

So, the answer is 643832