Collocations for understandable - adj.

be, seem
become

very
completely, entirely, perfectly, quite, totally, wholly
fairly, somewhat
His frustration is somewhat understandable.

certainly
It is certainly understandable that he would be so devoted to his home and family.

perhaps

be, seem
make sth
The author makes complex topics understandable by using simple words and examples.

easily, readily
She conveyed her knowledge in a way that was easily understandable.
Warning notices must be readily understandable.

to
The instructions must be understandable to the average user.

Understandable is used with these nouns:
anxiety, confusion, reaction, reason, reluctance