While solving the equation 4(x+2)=28, Becca wrote 4x+8=28. Which property did she use?

The original expression is $4(x+2)$.
Becca rewrote it as $4x+8$.

To transform $4(x+2)$ into $4x+8$, the number 4 outside the parentheses was multiplied by each term inside the parentheses ($x$ and 2).

Then these products were added together: $4x+8$.

This operation, where a factor outside parentheses is multiplied by each term inside the parentheses, is known as the Distributive Property.

The property Becca used is the Distributive Property.