We need to apply trigonometry for easy calculations.
Let Z represent the ramp.
sin x = wall divided by the ramp
Let x = 7°.
sin 7° = 2.5/Z
We now solve for Z.
Z = 2.5 ÷ sin 7°
Z = 20.5137726212
We round off to the nearest tenth of a foot. This means to round off to the ones place.
Z = 21 feet
Done.