Use Floor expression on a different Dataset

Hi

I need to use the Floor expression to get minutes showing as time so for instance I want 450 minutes to show as 7:30.  To do that I found the following on the internet

=FLOOR(Fields!NonChargeableMinutes.Value / 60) & ":" & RIGHT("0" & (Fields!NonChargeableMinutes.Value MOD 60), 2)

Which works fine the only issue is I want to show the cumulative NonChargeableMinutes underneath each staff member which is from a different Dataset.

Other Dataset is called "IllnessTotal" and the field is then Sum_NonChargeableMinutes

I tried the following

=FLOOR((Fields!Sum_NonChargeableMinutes.Value, "IllnessTotal") / 60) & ":" & RIGHT("0" & ((Fields!Sum_NonChargeableMinutes.Value, "IllnessTotal") MOD 60), 2)

But that doesn't work, can you get data from a different dataset when using the Floor expression?

I was originally using this

=LOOKUP(Fields!StaffId.Value,Fields!StaffId.Value,Fields!Sum_NonChargeableMinutes.Value, "IllnessTotal") / 60

But this then showed 450 as 7.5 which is not how the department I am doing the report for want it showing.  So ideally I would need the two combining?

Any advice massively appreciated.

Cheers

Chris

Cheers Chris