You will first have to change your text file so that ArcMap can understand it by adding a header:

The add it to ArcMap, which will interpret it as a table:

Use the Add XY events option to create point features with the appropriate coordinate system:

Followed by selecting the right fields:

and define the coordinate system (not sure if this the correct one in my screenshot below)

When you have the point events you can use the project tool to create a physical output featureclass with the WGS 1984 geographic coordinates:

and add coordinates:

to obtain the decimal degrees of the geographic coordinates as attributes in the featureclass:
