Probability – A fair die is rolled 100 times if the value is summed up

A fair die is rolled 100 times and the value on top of the die is summed (we'll call that sum X – note that X is between 100 and 600, inclusive). Calculate the mean and variance of X.

I am not looking for a complete solution, but looking for clues as to how to approach this question. I want to know how to get the value of X.