Mixture word problem

Question

A chemical company makes two brands of antifreeze. The first brand is 70% pure antifreeze, and the second brand is 90% pure antifreeze. In order to obtain 120 gallons of a mixture that contains 75% pure antifreeze, how many gallons of each brand of antifreeze must be used?

Answer 1

x gallons of .7

y gallons of .9

The system is :

x + y = 120

0.7x + 0.9y = 0.75*120

I think this way. You get 2 equations with 2 unknown vars.

Solve, get y = 30. Respevtfully, x = 120-30=90