Here's (b)....it's pretty much an extension of (a)
1000/7 = 142 numbers that have at least 1 factor of 7
1000/49 = 20 numbers that have at an additional factor of 7
1000/343 = 2 numbers that have a third factor of 7
So......... 142 + 20 + 1 = 163
And 7^163 will divide 1000! ...so n = 163