For the answer to the question above,
the given area of triangle, whose h = 6b +1 is equal 13 square feet
if the base is x which equation models the area
A = x*h/2
13 = x*(6x+1)/2
26 = 6x^2 +x
the equation which models area will be 6x^2 +x -26 =0
I hope my answer helped you.