How do you solve this ? y-2(3y-2)=-6

Really need on these. i have no idea what to do

The late fee for library books is $2.00 plus 15¢ each day for a book that is late. if maria’s fee for a late book was $3.20, write and solve a linear equation to find how many days late the book was.

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).