Expanding the first set of parentheses:

(x-3)(x+4) = x(x) + x(4) - 3(x) - 3(4) = x^2 + 4x - 3x - 12 = x^2 + x - 12

Expanding the second set of parentheses:

x(x+1) = x(x) + x(1) = x^2 + x

Putting everything together:

(x^2 + x - 12) + (x^2 + x) = 2x^2 + 2x - 12

Therefore, the final expression is:

2x^2 + 2x - 12 + x + 3 = 2x^2 + 3x - 9