Given the following balances, what is the most appropriate level of planning materiality for the 30 June 2022 audit of your client? (all amounts are in $'000)

Sales: 2792 (2022); 2512.8 (2021); 2233.6 (2020)

Profit: 124.4 (2022); 111.96 (2021); 99.52 (2020)

Current assets: 3640 (2022); 3276 (2021); 2912 (2020)

a. 27.9

b. 12.4

c. 36.4

d. 18.2