Solve the Problem Using Matrices $21 \%$ Copper to Make Jewelry $14 \%$

Multiple Choice

Solve the problem using matrices.
-Anne and Nancy use a metal alloy that is $21 \%$ copper to make jewelry. How many ounces of an alloy that is $14 \%$ copper must be mixed with an alloy that is $24 \%$ copper to form 100 ounces of the desired alloy?

A) $30 \mathrm { oz }$
B) $70 \mathrm { oz }$
C) $75 \mathrm { oz }$
D) $32 \mathrm { oz }$