Need help answering this question ​

Carlos has 4/5 of a tank of fuel in his car. he uses 1/10 of a tank per day. how many days will his fuel last?

How is working backward similar to solving an equation?

The graph of a function f(x)=(x+2)(x-4). which describes all of the values for which the graph is negative and increasing? all real values of x where x< -2 all real values of x where -2