I know that this is confusing. But basically, if A/B = C/D then A*D = B*C so if you have 20/10 = 60/D then you can solve that by multiplying 10*60 (which is B*C) which is 600 and now you know that 20*D = 600 so you divide 600/20 to get D, which is 30. Don't feel dumb for not understanding this. It's very complicated and I did a bad job of explaining it.
