Use the balanced scale to find the conversion factor that can be used to convert the number of blocks to the weight of the blocks in pounds.
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Find Total weight at left side
[tex]\\ \sf\longmapsto 6(1lb)=6lbs[/tex]
Now
Per block weight at right side
[tex]\\ \sf\longmapsto \dfrac{6}{4}=1.5lbs[/tex]