Assuming all apples, you should get 800 and actually get 660, so 140 is redundant, 140/( 10-6)=35kg pears. 35*6+45* 10
What you do is to assume that all pears are pears, and then you get 6*80=480, but what is 660-480 180 should be counted as apples, 180/( 10-6) The extra money of apples is 45.