Question 896396
h for height, b for base;
h=b-14.


{{{(1/2)b*h=520}}}
{{{(1/2)b(b-14)=520}}}
{{{b^2-14b=1040}}}
{{{b^2-14b-1040=0}}}
Note that discriminant is {{{66^2}}}
-
{{{b=(14+sqrt(66^2))/2}}}
and you can continue and finish this.


The quadratic equation in b is factorable but general solution is more comfortable here.