Answer
Fill the blank with:
factoring out
Work Step by Step
A formula is an equation inside which one of the variables (here: I) is the unknown. We want to isolate it on one side. In formulas we usually want it on the left side.
To isolate $I$ we factor the LHS:
$I(R+r)=E$
the next step is to divide with $(R+r)$, leaving I isolated on the left.
Fill the blank with:
factoring out
