If we were to view the ramp from its side, the profile would resemble a right triangle with a 90 degree angle where the sofa meets the floor.
In this case, the two legs of the right triangle are 55 inches and 28 inches, and we looking for the length of the hypotenuse.
We can use Pythagorean Theorem which states:

where a and b are the legs, and c is the hypotenuse.




c = 61.717 inches
To the nearest tenth, the answer is 61.7 inches.