The High low Method question 2

Got really confused as what was going on , also wonder if my calculator is Ok
Q
Activity levels 16000 2200
Total Costs 135000 170 000

once production reaches 17000 a cost of 5000 is applied
Calculate the Total cost at 20000 units

What I did and where I got confused

Worked out the Variable cost

22000 170000
-16000 – 135000
=6000 =35000

35000/6000 =5.83 ( Should I have rounded down?)

Finding the Fixed Costs 16000 x 5.83 = £ 93,280
22000 x 5.83 £128 260
Cost at 20000 = 20000 x .5.83 116,600

Fixed costs = TC 135000 – VC 93280 =41720
TC 170000 – VC 128260 =41740 ? there is a discrepancy of 20??????

To find the TC for 20000 unites at 5.83 Would be
Fixed cost + Variable + 5000
When I do this I get 41720 +116,600 +5000 = 163,320

the answers available were 163.000
and 160.000
could you tell me the correct calculation
Also is there a relationship between the variable cost and the added 5000

Thanks Charlotte

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