Step-by-step explanation:
To find the selling price, we need to calculate the profit and add it to the cost price, then add the GST.
Cost price (including GST) = K402.00
Profit = 80% of K402.00 = 0.8 x K402.00 = K321.60
Price after adding profit = K402.00 + K321.60 = K723.60
GST = 10% of K723.60 = 0.1 x K723.60 = K72.36
Selling price = K723.60 + K72.36 = K796.00
So, the selling price of the mobile phone is K796.00.