Hey there mate!
Please check the attached answer of picture for explanation.

Oh wait i got it give me a sec <span>To </span>calculate percentage<span> decrease: First: work out the difference (decrease) between the two numbers you are comparing. Then: divide the decrease by the original number and multiply the answer by 100. If your answer is a negative number then this is a </span>percentage<span> increase.</span>
A is possible because the two other sides combined are longer then six therefore can reach each other to create a triangle. b is not possible because 4 is the same length of 3 and 1 combined therefore will not create a triangle shape. hope this is what u where looking for(: