Khan Academy
Khan Academy: Equations With Parentheses: Decimals & Fractions
Solve linear equations that contain expressions with parentheses and the coefficients are rational numbers. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
Purple Math
Purplemath: Simplifying With Parentheses
Explains, with worked examples, how to simplify expressions which involve parentheses and variables, including how to take a negative through the parentheses.
Help Algebra
Help algebra.com: Getting Rid of Parentheses
Resource explains how to simplify several types of expressions that contain expressions using the properties of addition and multiplication and applying the properties with the order of operations.