Solve the Problem $\$ 30$ A Pound That She Wishes to Mix with 30 Pounds

Multiple Choice

Solve the problem.
-A merchant has coffee worth $\$ 30$ a pound that she wishes to mix with 30 pounds of coffee worth $\$$ 80 a pound to get a mixture that can be sold for $\$ 60$ a pound. How many pounds of the $\$ 30$ coffee should be used?

A) $20 \mathrm{lb}$
B) $25 \mathrm{lb}$
C) $50 \mathrm{lb}$
D) $10 \mathrm{lb}$