Okie so Mr Horiguchi's salary is THB75,000 and commutation allowance is THB5,000 for the period from 1 June to 31 July 2015 and after 1 August 2015, it will be decreased to THB1,000.
The calculation period is from 21 May to 20 July 2015 but for July it is from 1 June to 20 June 2015 so we need to carry out the calculation on a pro rata basis.