Angle1 = 90 degrees
Angle2 = 15 degrees
Angle3 = 75 degrees (because 180-15-90=75 and all angles equal 180 degrees)
Side1 = 300
Side2 = x (unknown)
Solve for x:
X / sin(15degrees) = 300 / sin(75degrees)
X = (300•sin(15degrees)) / sin(75degrees)
X = 80.38...
= 80
