8 1/4 *а - (3 1/6 *а - 1 1/15) = 8 1/4 *а - 3 1/6 *а + 1 1/15 = (5 +(1/4 - 1/6))*а + 16/15 = (5 + (3/12 - 2/12)) *а + 16/15 = 5 1/12 *а + 16/15 = 61/12 * а + 16/15
При а = 12/27 получим : 61/12 * 12/27 + 16/15 = 61/27 + 16/15 = 305/135 + 144/135 = 449/135 = 3 44/135