Question

Parallelogram ABCD ​ is a rectangle.

Answer 1

BD=AC=2CX
2y=2(3y-4)
y=3y-4
2y=4
y=2

Answer 2

we know that

If the parallelogram ABCD is a rectangle

then

$BD=AC\\AC=AX+CX\\AX=CX$

so

$2CX=BD$ ------> equation A

Substitute the given values in the equation A

$2(3y-4)=2y$

Solve for y

$6y-8=2y$

$6y-2y=8$

$y=2$

therefore

the answer is

$y=2\ units$