If the units for x are feet and the units for a x are pounds per foot what are the units for da dx O feet per pound per pound denoted ft lb lb O product of pounds per foot and feet that is pounds O pounds per foot per foot denoted lb ft ft O product of pounds per foot and pounds denoted lb ft lb O product of feet per pound and pounds that is feet O pounds per foot per pounds denoted lb ft lb What unit does La x a x dx have O feet per pound per pound denoted ft lb lb O product of pounds per foot and feet that is pounds O pounds per foot per foot denoted lb ft ft O product of pounds per foot and pounds denoted lb ft lb O product of feet per pound and pounds that is feet O pounds per foot per pounds denoted lb ft lb