Sin 30=y/7
y=3.5ft
You would start with your sin equation ( Sin angle= opposite side over hypotenuse)since you are trying to find the Opposite side length. So you would have sin 30 equals y over 7. Then you multiply over 7 to both sides.Last find the value of sin 30( sin 30=.5) and multiply that by 7, your answer is 3.5ft