"Their help is helpful."
Translation:Bantuan mereka sangat membantu.
Hai! I am not really sure. I think this sentence could be translated as "Their help is very helpful.", but as much as I know the Indonesian word "membantu" is a verb. Perhaps, it could be also translated as "Their help helps (or helped) a lot.", being "sangat" = very, a lot. Then, can be this the meaning of "helpful" (to help a lot)?
Since I cannot assure what English translation could fit better (my native language is Spanish), I can only say that, in these situations, it is always better to report the Indonesian and the English sentences as well, and trying also to add your suggestion as an alternative sentence. Then, try to mark all the possibilities in your report (including also the suggestions of the dictionary words) to make possible the contributors to read your report and see what they would change or not in this exercise.
Selamat belajar! :)
hi! sangat here adds emphasis. as diego noted already, it's use with the verb 'membantu' can be translated in various ways into english ...
'their assistance is very/ so/ really helpful' or 'their assistance really helps' or 'their assistance helps a lot'
btw 'assistance' would perhaps be a better choice of word to use in this example. while 'help' is also correct, it sounds a little oddly repetitive and unnatural to say 'their help really helps'.