This is the 10629th most frequent Spanish word.
cuán
"Cuán" means "how" or "how much" in English, used to indicate degree or extent.
Here, 'cuán' is used as an adverb to emphasize the degree of difficulty in resolving the problem, equivalent to 'how' in English.
No sabes cuán difícil fue resolver ese problema.
You don't know how difficult it was to solve that problem.
In this sentence, 'cuán' modifies 'lejos,' describing the extent or distance achievable, equivalent to 'how far' in English.
Cuán lejos podemos llegar depende de nuestro esfuerzo.
How far we can go depends on our effort.
'Cuán' is used to highlight the importance of his help, functioning as an adverb modifying 'importante' to signify intensity.