30-60-90 triangles are known to have a shortest side that is half of the length of the hypotenuse. Using that fact you can find that the hypotenuse has to be 4 feet in order for the shortest side to be 2 feet.
You can also use the fact that sin(30)=2/h in this triangle which means h=2/sin(30). Since you know that sin(30) can be thought of as sin(π/6), we know that sin(30) has to equal 1/2. That make it so that h=2/(1/2) which equals 4 feet.
I hope this helps let me know in the comments if anything is unclear.
