If you have one combination and n unused boxes, you have to find that box b where the value
Vb = Scoreb + probabilistic_valueremaining boxes b
is the biggest.
The problem here lies in two things:
There are in total 252 * 8191 = 2 064 132 different cases (number of distinct combinations * number of possible unused box combinations). Many of them are trivial, but many of them are not.
The probabilistic value of the remaining boxes includes the probabilistic value of the bonus too.
The simple answer for the question B - in case of a computer - is: choose the best value from the database. Unfortunately for human players we can’t give an exact answer or an easy formula to help, because 132 million different cases cannot be described in one sentence.
Hint: play and gain experience and keep an eye on the score needed for the Upper Section’s bonus!