Alloy c is made from some part of alloy a and alloy b.
alloy c, which weighs 400 ounces and has 40% aluminum, is obtained
from melting together x ounces of alloy a, which has 30% aluminum,
and y ounces of alloy b, which has 60% aluminum. which equation
will find how many of ounces of each alloy a and alloy b are used
to make alloy c?
a. a + b = 400
0.3a +0.55b = 0.4(400)

b. a + b = 400
30 a +55b = 0.4(400)

c. a + b = 40
0.3a + 0.55b = 400

d. a+b=400
0.3a+0.55b=400