Can someone please explain part b to me? I keep getting it wrong.

Compute the additional Medicare tax for the following taxpayers. If required, round your answers to the nearest dollar. a. Mario, who is single, earns wages of $523,200. His additional Medicare tax is s 2,909 b. George and Shirley are married and file a joint return. During the year, George earns wages of $183,400, and Shirley earns wages of $275,100 Their additional Medicare tax is X c. Simon has net investment income of $46,800 and MAGI of $234,000 and files as a single taxpayer. Simon's additional Medicare tax iss 1,292