Dreighton engineering group receives royalties on a technical manual written by two of its engineers and sold to william b. irving publishing, inc. royalties are 10% of net sales, receivable on october 1 for sales in january through june and on april 1 for sales in july through december of the prior year. sales of the manual began in july 2017, and dreighton accrued royalty revenue of $31,000 at december 31, 2017, as follows: receivable—royalty revenue 31,000 royalty revenue 31,000 dreighton received royalties of $36,000 on april 1, 2018, and $40,000 on october 1, 2018. irving indicated to dreighton on december 31 that book sales subject to royalties for the second half of 2018 are expected to be $500,000.