Given :
L = { ambncp | m + n + p >= 10 }
Lets think about language L' as : { ambncp | m + n + p < 10 }
Now this is clearly a finite language as there will be finite number of such <m,n,p> triplets..
Now let L'' = { a* b* c* }
Now clearly L = L'' - L'
Now as L'' and L' both are regular , hence L is also regular [ Also follows from closure property of regular languages]
Hence the given language is regular language..