Answer:
The mistake she made was ; She didn't change the sign when subtracting -3/4 from both sides
She wrote 5/4+3/4 instead of 5/4-3/4
Step-by-step explanation:
Correct solution:

Subtract-3/4 from both sides

Simplify

<h2>
Explanation:</h2>
In every rectangle, the two diagonals have the same length. If a quadrilateral's diagonals have the same length, that doesn't mean it has to be a rectangle, but if a parallelogram's diagonals have the same length, then it's definitely a rectangle.
So first of all, let's prove this is a parallelogram. The basic definition of a parallelogram is that it is a quadrilateral where both pairs of opposite sides are parallel.
So let's name the vertices as:

First pair of opposite sides:
<u>Slope:</u>

Second pair of opposite sides:
<u>Slope:</u>

So in fact this is a parallelogram. The other thing we need to prove is that the diagonals measure the same. Using distance formula:

So the diagonals measure the same, therefore this is a rectangle.
3(4)-7/y=1/3
12-7/y=1/3
-7/y=1/3-12
-7/y=-35/3
Change signs and cross multiply
21=35y
Y=3/5