A Merchant Has Coffee Worth $\$ 40$ A Pound That She Wishes to Mix with 60 Pounds

Multiple Choice

A merchant has coffee worth $\$ 40$ a pound that she wishes to mix with 60 pounds of coffee worth $\$$ 80 a pound to get a mixture that is worth $\$ 70$ a pound. How many pounds (lb) of the $\$ 40$ coffee should be used?

A) $20 \mathrm{lb}$
B) $40 \mathrm{lb}$
C) $80 \mathrm{lb}$
D) $10 \mathrm{lb}$