Wong Teasers, Week 13

[ProfessorBen]

Update: SF+3 is close to even money now on a couple of sites.

Question: I have a rough idea, but how do I tell how much it's worth buying an extra .5 to fully cross the 7?

ie. How do I calculate which option is better?
1: Team A +2/+8 teased with Team B +1/+7 at -110
2: Team A +2/+8.5 teased with Team B +1/+7.5 at -120

Also, I just wanted to check that the following prices were standard or good.
2 team: -110
3 team: +180
4 team: +300