Math question system of linear equations

Question

A chemist has three different acid solutions. The first acid solution contains 20% acid, the second contains 35% and the third contains 80%. They want to use all three solutions to obtain a mixture of 108 liters containing 40% acid, using 2 times as much of the 80% solution as the 35% solution. How many liters of each solution should be used?

Answer 1

0.2a + 0.35b + 0.8c = 108(0.4)

a + b + c = 108

c = 2b

0.2a + 0.35b + 0.8(2b) = 43.2

0.2a + 0.35b + 1.6b = 43.2

0.2a + 1.95b = 43.2

a + b + 2b = 108

a + 3b = 108

a = 108 - 3b

0.2(108 - 3b) + 1.05b = 43.2

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