Please help me to solve this question with explaination

Question

The Department of Health advised the public to sanitize their hands by using 70% alcohol solution as a measure to avoid the chance of getting infected by the virus. The head of the Pharmaceutical Company plans to produce more 70% alcohol solutions to respond to the demands of the people. As a chemist of the Pharmaceutical Company, you are tasked to make a report of the combinations of at least two alcohol solutions to come up with 200 gallons of 70% alcohol mixture. The only available alcohol solutions in the laboratory are 30%, 40%, 80%, and 90% solutions.

Answer 1

mix 30% with 90% to get 200 gallons of 70%

.9x + .3(200-x) = .7(200) = 140

.6x = 140 - 60 = 80

x = 80/.6 = 133 1/3 gallons of 90% mixed with 66 2/3 gallons of 30% will yield 200 gallons of 70%

or mix 30% with 80%

.8x + .3(200-x) = 140

.5x = 140-60 = 80

x = 80/.5 = 160 gallons of 80% mixed with 40 gallons of 30% yields 200 gallons of 70%

or mix 40% with 90%

.9x +.4(200-x) = 140

.5x = 140-80= 60

x = 60/.5 = 160 gallons of 90% mixed with 40 gallons of 40% yields 200 gallons of 70%

or mix 40% with 80%

.8x +.4(200-x) = 140

.4x = 140 - 80 = 60

x = 60/.4 = 150 gallons of 80% mixed with 50 gallons of 40% yields 200 gallons of 70%

or endless other combinations of all 3 or 4 percentages