Adding Rational Expressions

There is a mistake in the answer for the problem below. Work the problem yourself to determine the error. Correct the error, and explain how would you help another student who made that error.

\(\dfrac{4}{x-2}+\dfrac{3x}{x+3}=\dfrac{4(x-2)+3x(x+3)}{(x-2)(x+3)}\)