Calculate the standard enthalpy change for the reaction

Question

2A+B⇌2C+2D

Use the following data:

Substance ΔH∘f (kJ/mol)

A -251
B -403
C 213
D -511

My thoughts:
[(2)(-511)+(213)(2)]-[(2)(-251)+(-403)]=309kJ
(but apparently that is not the correct answer)
What did I do wrong?!?!?

Answer 1

I don't see anything wrong with what you have.

Answer 2

its supposed to be C+D-B-C

Answer 3

309