The quadrilateral have equal opposite sides, for example:
Then, (4x + 6) must be equal to (7x - 3), and (4y - 3) is equal to (3y + 1), therefore

We can solve that equation for x

Hence, x = 3. Now let's solve the other equation

Then the value of y is 4.
Final answers:
x = 3
y = 4