Fixed/variable/semi variable

LA2018

Help!
Completely stuck on how to figure out the attached. I get the fixed costs but how do I know the difference between variable and semi variable? I just don’t know how to work it out like this.

dumutroba

Variable increase proportioned to the units increase, unit cost is the same, unlike the semi-variable
2000/6000 =0.3 and 9000/27000 =0.3 this is variable
Fixed as you have said is obvious, the total cost is the same - £6000
The middle must be semi, we can check with high low method
Variable element is £1
1500x1=1500
2500-1500=1000 fixed element
Check, 3500x1=3500+1000=4500