Question 1150741
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We have three unknowns and only two equations, so it looks as if there is not enough information to solve the problem.<br>
However, the problem does not ask us to solve for a, b, and c.  It only asks us to find the value of 2a^2-3b^2+c^2.  It turns out the problem is contrived so that it is possible to do that.<br>
One piece of given information relates the values of a and b; the other relates the values of b and c.  The common variable there is b.  So use those pieces of information to find expressions for a and c in terms of b and substitute them in the expression to be evaluated.  It will turn out that all the variable terms cancel out, leaving you with a numerical value for the expression.<br>
{{{a+b = -3}}}  -->  {{{a = -b-3}}}
{{{b-c = 6}}}  -->  {{{c = b-6}}}<br>
{{{2a^2-3b^2+c^2 = 2(-b-3)^2-3b^2+(b-6)^2}}}<br>
Expand and simplify to find the answer....<br>