how many psitive integers x are such that 3x has 3 digits and 4x has 4 digits?

three digit numbers are 100 to 999 = 3x …............(1)
four digit numbers are 1000 to 9999 = 4x …..........(2)

so from (1) 33.33<x <= 333
and from (2) 250 <= x < 2499.75

x = 250,251, 252, ….....,333

333 = 250 + (n-1)1
so n =84

Thanks