$($b$)$ Suppose you start the trip by riding in the wrong direction $($with the same constant speed as above for the first part of the trip$)$ and after traveling a distance d $($in the wrong direction$)$ you realize your mistake. If you then ride to the correct destination with a constant speed, what must this speed be in order for the time for the total trip ttb for case $($b$)$ to be $1\mathrm{.}80$tta, where tta is the time for the total trip in part $($a$).($Enter your answer to at least one decimal place.$)$