Let's simplify the given expression:

First, let's simplify (X2-3x)/2:
(X2-3x)/2 = X(X-3)/2

Next, let's simplify (x2-3x)/2:
(x2-3x)/2 = x(x-3)/2

Now, let's plug these values back into the original expression:
(X(X-3)/2 + 3)(x(x-3)/2 - 4) = 3

Expanding the expression, we get:
(X^2 - 3X + 6)(x^2 - 3x - 8) = 3

Solving further, we get:
X^2 x^2 - 3X x^2 - 8X^2 + 6x^2 - 18X + 48 = 3

Combining like terms, we get:
X^2 x^2 - 3X x^2 - 8X^2 + 6x^2 - 18X + 48 - 3 = 0

Simplifying the equation, we finally get:
X^2 x^2 - 3X x^2 - 8X^2 + 6x^2 - 18X + 45 = 0

Therefore, the simplified equation is:
X^2 x^2 - 3X x^2 - 8X^2 + 6x^2 - 18X + 45 = 0