You can put this solution on YOUR website! I'm assuming that (155)16 represents 155 in base 16. If I am wrong then you will have to re-post your question (making it clearer).
Our numbering system is based on place values. And the values of the places represent various powers of the base:
The value of the rightmost digit is the base to the zero power.
The digit to the left of that has a value of the base to the first power.
The digit to the left of that has a value of the base to the second power.
etc.
So 155 in base 16 stands for:
Simplifying...
So 155 in base 16 is equal to 341 in base 10.