Maybe to be safer use formula in C38:

=SUMIF(C16:C31,">="&$F$11-90,F16:F31)-SUMIF(C16:C31,">"&$F$11-60,F16:F31)

and in D38:

=SUMIF(C16:C31,">="&$F$11-60,F16:F31)-SUMIF(C16:C31,">"&$F$11-30,F16:F31)

leave the others as are.