Lara drew a figure in order to show how to complete the square for the expression x2+7x. She started with a square with side lengths of x to show the x2 term.
She then added two rectangles to the sides of the square. One rectangle had a side length of 4 units and an area of 4x square units, and the other rectangle had a side length of 3 units and an area of 3x square units. These rectangles together have an area of 7x square units.
Finally, she filled in the rest of the figure with a rectangle that had an area of 12 square units.
The following figure is Lara's final figure.
What mistake, if any, did Lara make?

1. Lara should have added rectangles with areas of 5x square units and 2x square units instead of 4x square units and 3x square units.
2. Lara should have added rectangles with areas of 3.5x square units and 3.5x square units instead of 4x square units and 3x square units.
3. Lara did not make a mistake.
4. Lara should have added rectangles with areas of 16 square units and 9 square units instead of 4x square units and 3x square units.