8x+3=a
8y+7=b
ab/8=(8x+3)(8y+7)/8=(8x+3)(8y+7)/8=8xy+3y+7x+21/8=8xy+3y+7x+(16+5)/8=8xy+3y+7x+2+5/8
=> остаток 5
8x+3=a
8y+7=b
ab/8=(8x+3)(8y+7)/8=(8x+3)(8y+7)/8=8xy+3y+7x+21/8=8xy+3y+7x+(16+5)/8=8xy+3y+7x+2+5/8
=> остаток 5