How do you calculate double-taxed income for DC and MD when you have separate W2's for those two states? Where can I find/calculate that and the 'tax paid' question?

Hi, 

In 2017, I was a part-time resident in DC and a full-time resident in MD. I have a W2 from my employer for each state. How do I determine if I have double-taxed income? How can I find how many taxes I paid to Maryland and/or DC on double-taxed income? Do I have to fill out that double-taxed info for both my DC and MD 2017 return?

Thanks much, 
Jackie