Mathematical problems are solved by equations.

1, because the charges of the two companies are the same, it is assumed that the charges of the two companies are X.

Then the total cost of Company A is 5x+20x70%x= 19x.

The total cost of Company B is 25x80%x=20x.

Therefore, they choose company A, with less travel expenses!

2. Suppose they went to X adults and 12-x students.

Then 35x+( 12-x)x35x50%=350.

x=8 12-x=4

They went to eight adults and four students.

Hope to adopt, thank you! !