howdy there annephilbrick! sorry I've been away from my computer today and I see that your wrote this 3 hours ago.
ok, I suggested that you put 75 into the box for Steem Power Wanted and when you do that then put in 4 weeks in the next box down and then it should tell you how much steem that will cost and if you're ok with that you just hit the Lease button. I think 75 sp costs 2 steem and that should get you plenty of rc power but if you want to make sure then make it 90 or 100 sp.
I hope this helps but shoot me another comment if you have more questions!