Question 970998
{{{2a+b=15.7}}}
{{{b=-2a+15.7}}}


These are important restrictions:
{{{0<02a+15.7<15.7}}}
and you can solve this for a.  

Corresponding to the set of max and min for a, find b.


See among the choices that two of them make no sense at all.
I leave actually answering the question to you; I just gave partial steps and guidance.