Lebesgue measure of a set

Let m the n-dimensional Lebesgue measure on $R^n$.By definition of product measure, on each borelian set E

$m(E)=inf left(sum_{j=1}^infty m(R_j),:: Esubseteq bigcup R_j , ::R_j text{ rectangles}right)$

It is also true that lebesgue measures are regular, so
$m(E)=inf left(m(U), Esubseteq U, : U text{ open set} right)$.

Can I say that also holds
$m(E)=inf left(sum_{j=1}^infty m(B_j),:: Esubseteq bigcup B_j , ::B_j text{ balls}right)$ or not?

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