Dia daoibh a chaire,

An bfhuil sé seo ceart go leor?

"Is iomaí an dúshlán roimhe an múinteoir" There's many a challenge before the teacher ?

GRMA

Is iomaí dúshlán atá roimh an múinteoir maybe?

Is iomaí dúshlán os comhair an mhúinteora.

For the use of "is iomaí" and other expressions, one can think of what is said in songs.
You can think of the following, to know how "is iomaí" is used:

Is iomaí fear a d'úrt liom
Monuar gan tú sa bhaile agam

(in A stór a stór a ghrá, as sung by Altan)

ie. noun without the article, and in the nominative singular

_________________
Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

I use songs as mnemonics in much the same way!