NoDictionaries   Text notes for  
... operis uestri quam emolumenti rationem exactam, milites, habet; oppugnabitis...

That is, the advanatages/benefits (emolumenti) of taking the city will exceed the effort (operis); The core idiom here is rationem habere (+ genitive), which means "to take account of" or "to have regard for" something. Contextual Meaning in the Speech Scipio is employing a rhetorical cleverness here: he tells his men that while taking the city might look like a task requiring enormous effort (opus), the actual tactical effort needed will be surprisingly light, whereas the gain (emolumentum)—the capture of Spain’s wealthiest stronghold—will be disproportionately vast. The "reckoning" or "proportion" (ratio) works entirely in the soldiers' favor.