Conditional formatting cells, dependent on value in range and choice of drop down list

I have the below conditions i want my cells to relate to.

Picture1.jpg

I have a column with all my data in, and in the column next to it i have a drop down list for the severity, (1-6), which can change and I choose manually.

I want the cell with the data in to be formatted the same as the image. So if the value is in the range >=10E-4 to <10E-3, and I specify the severity is a 5, then my cell with data in goes yellow, and if its a severity of 6 then the cell becomes red, etc.

all ideas will be really helpful.