Look at the triangle as a whole. This is a 30-60-90 triangle by speculation. You can see that the hypotenuse is equal to 100. By using sine (you can use cosine as well) , you get the expression, "(sin 30 degrees) = x/100" since sin is the opposite side over the hypotenuse. Do some basic trigonometry to get "1/2 = x/100". By now, you should know that 50/100 is the same as 1/2.
