'it was fairly difficult' is a correct and usable phrase in written English.
You can use it whenever you want to indicate that something was moderately challenging. For example: "I thought the exam was fairly difficult, but I'm sure I passed."
"It's fairly difficult to counterinvade their space," Mr. Osha said.
"It's fairly difficult to believe in this comeback, but anything is possible in football," the striker said.
It is fairly difficult today not to have a footprint – or a faceprint, given the sophistication of facial recognition technologies – on the Internet.
It is fairly difficult to evade taxes on legitimate investments because the I.R.S. can crosscheck the forms supplied by the company and the individual.
It's fairly difficult to achieve an effect of coziness in such vast, echoing spaces, although we were given a glimpse of the Presidential slippers under the Presidential bed.
"In reality, there's lots of other people posting information about you without your control and it is fairly difficult – if not impossible – to police the social media circles of everyone you know," says Marwick.
The idea of reworking Dylan songs might seem as futile as rewriting Wuthering Heights given that it's fairly difficult, looking back over more than half a century, to think of more than a couple of Bob Dylan cover versions that are even faintly as interesting as the original.
In practical applications, however, spectra obtained include so many peak frequencies that it is fairly difficult to identify the defect correctly.
In spite of the multiple advantages, it is fairly difficult to maintain a desired level of QoS for multimedia applications in a multihop network like WMN.
