



 
Hi Carol. Write out the question using variables and you'll see what you need. Let a = the length of one side of aluminum Then the area is: The cost of the aluminum is (2)a(20) = 40a and the steel costs (2)s(10) = 20s. The total cost is: Now you have two equations with two unknowns. Use any of the usual techniques (such as the substitution or elimination method) for solving this system of simultaneous equations. You will need to factor the quadratic (or use the quadratic formula if you can't see how to factor it) and you will find that there are two answers to this question! Hope this helps,  


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