Enable option button contingent on other cell values

I have this speadsheet and I want the "Desktop Valuation" option button to be enabled when "Standard" option button is selected and cell E12 is less than or equal to $250,000. I also want it to be enabled if "Standard" option button is selected and "Renewal/Existing" option button is selected (no matter the value in cell E12). I want it to be disabled any other time. I Believe the part of code that effects this is in Sheet 1 (Request Form) and scroll down to Private Sub Standard_Click() section. Thanks.