А)не понял
б)2 8/15+у=-1 7/10
у=-1 7/10-2 8/15
у=-4 7/30
1 7/10 + 2 8/15 = 3 + 7/10 + 8/15 = 3 + 7·3---10·3 + 8·2---15·2 = 3 + 21/30 + +16/30 = 3 + 21 + 16/30 = 3 37/30 1710 + 2815 = 3 + 710 + 815 = 3 + 7·310·3 + 8·215·2 = 3 + 2130 + 1630 = 3 + 21 + 1630 = 3 37/30 = 4 7/30