How can all of us be there simultaneously #1? - A Hard Physics Problem

3 people (let's name them Adam, Ben and Cathy) are in place A and have to be in place B simultaneously. The distance between A and B is 20 km. They have a bike which can hold only 2 people or less. They know how to do it. At first, Adam and Ben travel by bike and Cathy walks. When Adam and Ben reach a point C, Adam uses the bike to return to Cathy at a point D meanwhile Ben walks to B. When Adam reaches D, Adam and Cathy turn back and travel by bike to B. All 3 people finally reach B simultaneously.

How long do Ben and Cathy walk until Adam Ben, Cathy reach B? How long does Adam travel by bike until Adam Ben, Cathy reach B?

The answers to the first question are $t_{2}$ and $t_{3}$ . The answer to the second one is $t_{1}$ . Type $t_{1}+t_{2}+t_{3}$ to the first decimal.

Note: All motions mentioned in this problem are linear motions.