Cash Receipts Gross income from patient consultations at the medical practice: $90,000 As a supply of medical services is GST-free in Australia under Section 38-7 of the GST Act 1999 (Cth), there is no GST to account for in this income. Gross income from the charter boat business: $27,000 Since it satisfies all the criteria of taxable supply under s. 9-5 and it's not a GST-free or input taxed supply, a charter boat business can be considered a supply for GST purposes. Therefore, gross income from the charter boat business is subject to 10% GST. $27,000 x 1/11 = $2,454.54545 Thus, Dr. Shishya has GST payable of $2,454.54545