Yes, they have multiplied April sales by 95% but only the credit sales that were paid within the 14 days: Credit sales: ‘Apr sales 58,000 x 80% x 40% x 95% 17,632’
However, for the 20% of cash sales, it appears they have simply taken the total cash sales and multiplied it by 20% and have not accounted for the 5% discount. Cash sales: ‘April 20% x 58,000 11,600’.