help solving problem

Question

A chemist mixed a 70% alcohol solution with a 30% alcohol solution to make a 45% alcohol solution. How many liters of each were used to make 120L of a 45% alcohol solution?

a. 75L of 70%, 45L 30%

b. 18L of 70%, 102L of 30%

c. 45L of 70%, 75L of 30%

d. 22.5L of 70%, 97.5L of 30%

Answer 1

s=ml 70%

t=ml 30%

s+t=120

.7s + .3t=.45*120

Multiply the 2nd equation by 100 and the first equation by 30

30s + 30t = 3600

70s + 30t = 2400

40s=1200

You finish it from here.