PARTA HK Furniture sells mattress with a 5-years warranty at a selling price of RM1,100 per mattress excluding 6% sales tax. Past experience indicates that 3% of the units sold will be returned during the warranty period for exchange. The average cost to repair one mattress under warranty is estimated to be RM420 per unit. During the year 2021, HK Furniture sold 400 units of mattress and repairs were made on 75% of the estimated units returned. Total cost of repair were as estimated. Required: Prepare journal entries to records: (Show your workings) (a) Sales revenue and sales tax payable in 2021 . (b) Estimated warranty expense for the year 2021 . (c) Repairs made under warranty for the year 2021