Carefully placed on top of each other—one by one—the rocks used in this tower are able to avoid toppling from the pull of gravity because they are a balanced mass. Any shift in either direction from wind, erosion, any other force could cause the tower to fall. In this section, we will solve equations by keeping quantities on both sides of an equal sign in perfect balance. We will practice using mathematical rules of equality to unwrap the equation and solve for the unknown quantity.