Hey There
In multiplication you have to know the process of regrouping, which means to take away from tens. Also, you multiply from left to right.
Steps
1. First multiply 55=25, the two adds to the product of 52
2. Now you have to multiply 52=10, now you have to add two because of regrouping, 10+2=12, so you're final answer is 125.
In conlusion, 255=125
Hope this helps :)