Cut the sign in half across its middle. Then you have two right triangles.
They're congruent, so pick one to work with, and discard the other one
temporarily.
In the right triangle:
-- The length of one leg is 'x'.
-- The length of the other leg is (2x + 7).
-- The length of the hypotenuse is 35.47 inches.
You know that in any right triangle:
(The square of the hypotenuse) =
(the square of one leg) + (the square of the other one.)
so you can use that to find the value of 'x'.
One you know the value of 'x', go back to the whole sign before you cut it
in half, and notice that the height of the sign is '2x' ... which is the answer.