adding to formula revised

how can i add -(q10:q11) to the following formula with out returning #VALUE in cell N9, n9 is where this formula is

=IF(AND(ISBLANK(D9),ISBLANK(E9)),"",IF(24*(IF(E9>D 15,D15+2-E9,D15-E9))=0,24,24*(IF(E9>D15,D15+3-E9,D15-E9))))

i have tried adding the following to the formula -(q10:q11)

but does not work

please download my work sheet to see what i mean

q10 and q11 do have formulas in them.