IF Statement Won't Work As I Have Exceeded The Limits

I have been trying to do an if statement but need to choose between 10 options:

In Column AA I could have any one of the following 10 text entries - In column AB I need to return 8, 4, 2, 1 or 0.5 depending on which is in AA (this column AA cannot be sorted nor are people willing to cut back to 5 options )

"Very High" returns 8
"Very High (>50)" returns 8

"High" returns 4
"High (>20)"returns 4

"Medium" returns 2
"Medium (>10)" returns2

"Low" returns 1
"Low (>5)" returns 1

"Very Low" returns 0.5
"Very Low (<1)" returns 0.5

naturally the following IF statement won't work as I have exceeded the limits