What should be added to 3(x−2y) to obtain 2(3x+y)−5(2x+3)?

Let the expression to be added be A.
According to the problem:

3(x−2y)+A=2(3x+y)−5(2x+3)
First, simplify the target expression on the right-hand side:

2(3x+y)−5(2x+3)=6x+2y−10x−15=−4x+2y−15
Next, simplify the initial expression on the left-hand side:

3(x−2y)=3x−6y
Now, substitute back into the equation:

(3x−6y)+A=−4x+2y−15
A=(−4x+2y−15)−(3x−6y)
A=−4x+2y−15−3x+6y
A=−7x+8y−15
A=8y−7x−15