Not sure about the summer part, but the answer should be 1 / 6. Maybe your question is wrong.
Answer: 
Step-by-step explanation:
You must draw a right triangle as the one attached, where "x" is the lenght in feet of the ramp.
You need to use the following Trigonometric Identity:

In this case you can identify that:

Now you must substitute these values into
:

Finally, you must solve for "x" in order to find its value.
This is:

twice the sum of a number and 3, means you need to add the number to 3 first, then multiply by 2.
The correct expression would be 2(n+3)