Which represent the share is a rhombus if and only if the dangles are perpendicular and the sides are congruent

  6

Step-by-step explanation:

6 is the value that is added to the variable term. To isolate the variable term, 6 must be subtracted (from both sides of the equation).

Comment on the question

You can also think of it as adding the opposite of 6. The idea is to "undo" the addition of 6. In general, you solve equations by "undoing" what is done to the variable.

The properties of equality tell you that the equation will remain true (the value of the variable will not change) if the same quantity is added, subtracted, multiplied, or divided on both sides of the equal sign. Thus, if we say "subtract 6 from the equation", we mean "subtract 6 from both sides of the equation."

Beware of any advice that suggests you do something different to one side of the equation or the other. Such advice is probably wrong, or incorrectly stated.