Final answer:
According to the law of supply, if the electronics store could sell the headphones for $120 without losing customers, there would be a surplus of 145 pairs of headphones per month.
Step-by-step explanation:
According to the law of supply, if the electronics store could sell the headphones for $120 without losing customers, there would be a surplus. To determine the quantities demanded and supplied at a price of $120, we need to compare the original price and quantity with the new price and quantity. The original price is $100 and the original quantity demanded is 5 pairs per day. Assuming the demand remains the same, at the new price of $120, the quantity demanded is still 5 pairs per day. On the supply side, the store purchases 150 pairs of headphones per month from their suppliers. Assuming the supply remains the same, the quantity supplied at the new price of $120 is still 150 pairs per month. Therefore, at a price of $120, there would be a surplus of 145 pairs of headphones per month, meaning the quantity supplied exceeds the quantity demanded.