She is correct.
120-36=84=2^2*3*7
The key is to notice that if the two numbers are a and b, then gcf(a,b) | a-b ---> this means that the greatest common factor of a and b divides their difference. Also, a-b> gcf(a,b)
So, the only case to consider is if gcf(a,b)=2 and a-b=42.
This is clearly possible to find 2 such numbers a,b (one example would be 62 and 20).
