Question 1021644
If the equation is correct, just solve for h.  Maybe general form is factorable or maybe not.


The bases are lengths h+3  and  h+7; so the average is  {{{(h+3+h+7)/2=(2h+10)/2=h+5}}}, and the trapezoid area will be  {{{(h+5)*h=245}}}, since the area is given.


As already stated, either {{{h^2+5h-245=0}}} is or is not factorable.  Since you are told use quadratic formula, ...
{{{h=(-5+- sqrt(5^2-4*(-245)))/2}}}
Simplify and choose what value makes sense.