How many liters each of a 20% acid solution and a 50% acid solution must be used to produce 50 liters of a 35% acid solution?

Ijust need these 2 questions answered (the second pic is just confirmation i'm not confident in that answer)

How can writing phrases as algebraic expressions you solve problems?

Were only 64 seats. the remaining 6 students had to travel in a separate van. the equation 2b + 6 = 70 represents the given scenario. what does b represent? the number of buses the number of vans the number of students who rode on each bus the total number of students going to the football game