Yup, Following up on Marcster’s post, here’s one way to write the measure:
Sum of T Value for 4X Accounts =
LEFT( Data[Account], 1 ) = "4"
Note: I wasn’t sure whether you meant T value in a formal statistical sense, or whether that was a stand-in for just some measure in your report. Thus in this example, my “T Value” measure is deviation from the mean, just for illustrative purposes.
I hope this is helpful. Full solution file attached.