They face formidable challenges.
Times, Sunday Times (2016)
The concert he's talking about is a formidable challenge for a man who's been learning the piano for less than two years.
Times, Sunday Times (2013)
This is a formidable challenge for historians, because the technical difficulties of studying past migrations are imposing.
Migrants in Modern France: Population Mobility in the Later Nineteenth and Twentieth Centuries (1989)