For this, you will be doing the pythagorean theorem, which is
. In this case, the legs are 12 and 35 and the hypotenuse is AB. Using this, the equation will look like this:

Firstly, solve the exponents: 
Next, add up 144 and 1225: 
Lastly, square root each side, and your answer should be 
In short, the hypotenuse is 37 ft, or the last option.