Chemistry help?Ambiguity in question?

2NO2 <=>(equilibrium sign) N2O4 heat of combustion[∆H]= -58kJ/mol My question is, that when I was doing a past paper, it asked me to identify whether the forward reaction is exothermic or endothermic. The thing is that they never mentioned that the heat of combustion[∆H] was for the forward or backward.... show more 2NO2 <=>(equilibrium sign) N2O4 heat of combustion[∆H]= -58kJ/mol

My question is, that when I was doing a past paper, it asked me to identify whether the forward reaction is exothermic or endothermic. The thing is that they never mentioned that the heat of combustion[∆H] was for the forward or backward. So, I just randomly guessed the forward reaction was exothermic, and as a matter of fact , I was right. But, when another question comes up, like this one, how do I know which ones exo or endothermic when the question itself is this ambiguous.
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