Are hyenas solitary

Answer 1

No, they are cowards and are not very strong. You could compare a hyena to a normal house dog.

Answer:
Let's use the spotted hyena (the largest hyena) as an example:

• They have powerful forequarters and necks which similar to those of leopards.

• The males are smaller than the females both in shoulder height and weight. The biggest specimens have been about 81,7 kg (180 lb)
  

• The teeth are bone crushers and much stronger than those of dogs and wolves, bears, lions or leopards. Their bite exerts a pressure of 800 kgf/cm2 (11,400 lbf/in²)

Altogether a formidable animals far outclassing most common species (dogs, bears etc.) that you might have contact with.
As far as hunting alone, yes they do. By nature they are pack animals but sometimes go off hunting solo.
As far as being cowards, hey are smart enough to sty out of harm's way, but will kill and eat a wide range of prey including people.

Answer 2

Hyenas live in clans of up to around 90 individuals, and yes, will hunt in packs, but also alone.