The simplest way would be to use a calculator to evaluate B = arcsin(0.7245)
If you don't have a calculator, the next, more complex way would be to interpolate a table of sines and find the value of the angle whose sine is 0.7245. That is the method that was most widely used before the invention of hand held calculators and after sine tables had been published.
The next, most complex way would be to evaluate terms in the infinite series representation of the arcsine function which is the way the sine tables were developed for publication. That series is
arcsin(x) = x + x³/6 + (3/40)x^5 + (15/336)x^7 + ...
The result for any of those methods would be B = 46.4°
Geometrically, you could:
1) Draw a circle of known radius, R. centered at the origin of a rectangular coordinate system
2) Draw a line parallel to the x axis a distance 0.7245R above the x-axis
3) Draw a line connecting the origin to the rightmost point of intersection between the circle 1) and the line 2).
4) Measure the angle between the line 3) and the +x axis.
The Angle 4) will be the measure of the angle whose sine is 0.7245.
That explains four ways you can find the measure of the angle whose sine is 0.7245.
