"You eat breakfast."
Translation:Itheann tú bricfeasta.
You might be thinking of present tense verbs where, for example, you would not say 'itheann mé' you would say 'ithim', the same with 'we' - 'itheann sinn' is incorrect but 'ithimid' is correct. The 'mé' and the 'sinn' get put into the verb. Hope this helps!
Yes 'itheann sibh bricfeasta' is also present tense. Sorry for the confusion. The only time the person is included in the verb is 'mé' e.g. 'ithim' or 'sinn' e.g. 'ithimid'. Don't worry if you find Irish grammar confusing. sometimes I find it confusing and I've been learning it since I was 5. (I'm Irish)
In the present tense, the only forms that include the subject are the first person singular and plural forms--and those forms aren't used everywhere--people will say itheann muid, for example. So--you have to have the verb ending -im or imid or a separate subject. (In the present tense.)
You have to be really careful about spelling. If you just have one letter or so wrong, they usually let it slide, unless your misspelling would be a different word--so misspelling big as bik would probably be okay, but not misspelling it as bug. The correct answer is * Itheann tú bricfeasta*, and I guess you just missed too many letters. :(