5/18+7/12=10/36+21/36=31/36 4/17-20/51= 12/51-20/51=-8/51 31/36* 2 целых 10/31=31/36*72/31=2 1 целая 13/51 : -8/51=64/51 * - 51/8= - 8 2-8= -6 Ответ: -6