Firstly, i'll note that 7000 is a multiple of 7.
So we'll start from there.
The previous multiple of 7 will be obtained by substracting 7 to 7000, and so on.
So if you divide the interval into intervals of 7 numbers, ]a;b], these interval will contain one and only one multiple of 7.
Hence you "just" have to see how many intervals of this sort there are in [4500;7000], and this number is given by (7000-4500)/7.