4) 6,4/5-2,3/8=; 5)9,1/2-4,3/8= ; 6)8,19/20-5,7/10=

6 4/5-2 3/8=6 32/40-2 15/40=4 17/40
9 1/2-4 3/8=9 4/8-4 3/8=5 1/8
8 19/20-5 7/10=8 19/20-5 14/20=3 5/20=3 1/4