When converting moles to an element, say water, how do you determine which element gets divided by which when trying to determine the number of moles?

I'm working on mastering chemistry and trying to understand how to do it, and the question was:

Calculate the mass of water produced when 6.59 g of butane reacts with excess oxygen.

I understand first you convert the mass of butane to moles, than you calculate the number of moles to water by looking at the coefficients in the balanced equation.

So essentially its: 0.113mole C4H10 × 10 moles H2O divided by 2 moles C4H10 = 0.565 mole

**But how do you determine which element gets divided by which?**

Like how do I know I'm not supposed to divide butane by H2O instead?

Sorry it's been a while so this is all new to me.