so either x=0 or x=5/3
if x is an integer then it can be any integer not necessary a '0' [i.e. it can also be a 1,2,3,4,5]
so this is NOT SUFFICIENT alone.
Now the second statement says that the product of x and positive integer y is not x. that means x is definitely not zero. But again this statement does not tell us whether x is '5/3' or not. so NOT SUFFICIENT
But if we club both the statements together we come to know that the problem statement is not true.[i.e. (4^x )^5-3x is not equal to 1]
So both the statements together are sufficient.