Every equation on this sheet takes two moves to solve: 3c + 4 = 25, or c ÷ 3 - 2 = 4. Undo the addition or subtraction first, then the multiplication or division - the reverse of the order they were applied in.
That reversal is the whole lesson, and it is why two-step equations are taught separately from one-step ones. A student who has one-step equations automatic can still get these wrong by undoing in the order they read them.
Work backwards. In 3c + 4 = 25, subtract the 4 first to get 3c = 21, then divide by 3 to get c = 7. Undoing in the other order does not work.
Because the equation was built the other way round: c was multiplied by 3 and then 4 was added. Undoing runs the steps backwards, which is why the last thing done is the first thing undone.
Yes, and nothing goes negative on this page. Turn on Negative Numbers under Advanced options for the version where solutions can be below zero.
Seventh grade. It follows one-step equations, which are sixth.