Answer
$x=\dfrac{u+2v}{5}$ and $y=\dfrac{3v-u}{10}$
Work Step by Step
Consider $u=3x-4y$ and $v=x+2y$
Given: The parallelogram with vertices $(0,0), (4,3), (2,4), (-2,1)$.
which in the form of the equations as follows: $-10 \lt 3x-4y \lt 0$; $0 \lt x+2y \lt 10$
or, $-10 \lt u \lt 0$ and $0 \lt v \lt 10$
This represents a rectangle in the $uv$ plane.
Now take the assumptions such as: Multiply $v=x+2y$ with $2$ and then take sum with $u=3x-4y$.
we get $3x-4y+2x+4y=u+2v$
$\implies x=\dfrac{u+2v}{5}$
Also, $v=x+2y$ with $-3$ and take the sum with $u=3x-4y$.
we get $3x-4y-3x-6y=u-3v$
This implies that $y=\dfrac{3v-u}{10}$
Hence, $x=\dfrac{u+2v}{5}$ and $y=\dfrac{3v-u}{10}$
