The answer would be:
20.9 ft
Here is why:
If you draw the scenario, (which is attached below) you can see that a right triangle is formed. The ramp length is the hypotenuse of the scenario. To solve for it, we can use the Pythagorean Theorem where:
![c^(2)= a^(2) + b^(2)](https://img.qammunity.org/2019/formulas/physics/high-school/yh3z1fspj9vfujolgyky35emn7mufuw8yf.png)
Where:
c = hypotenuse (Longest side)
a and b = legs of the triangle
Let's take our given and put it into the formula:
c = length of the ramp
a = 6ft
b = 20ft
![c^(2)= (6ft)^(2) + (20ft)^(2)](https://img.qammunity.org/2019/formulas/physics/high-school/qhxgqy1hq41rvy8ioskqufchkjug942h70.png)
![c^(2)= 36ft^(2)+ 400ft^(2)](https://img.qammunity.org/2019/formulas/physics/high-school/uffx696y5noooflwm1ivvguw5kg8tyjqw1.png)
![c^(2)= 36ft^(2)+ 400^(2)](https://img.qammunity.org/2019/formulas/physics/high-school/2s3h4ah19swbga5vuml94l83ptabezaww9.png)
![\sqrt{c^(2) } = \sqrt{436ft^(2)}](https://img.qammunity.org/2019/formulas/physics/high-school/u2ei39a8e6pl79fturrbo0s2yfmphrabjh.png)
![c= 20.9ft](https://img.qammunity.org/2019/formulas/physics/high-school/o9m74r644443uwvo8yt5yvsbe07cke53g5.png)
Hope you get it!