[erased due to error made]
well, i finally found the review that we did in my class (i was trying to do the problems again for more practice, and thought i left it at home) and we went to (4x)^3 - (y^2)^3 and then did the difference of cubes. it came out to be (4x - y^2)(16x^2 + 4xy^2 + y^4)... and i had the first problem wrong, that is probably why... it was 64x^3 - y^6 and not y^4... that was my bad