Sohcahtoa.
Sine = Opposite/Hypotenuse
Cosine = Adjacent/Hypotenuse
Tangent = Opposite/Adjacent
So we need to find out he sine of angle A. So what is the opposite of angle A? 8
Now we need to find the hypotenuse. The hypotenuse is always across from the right angle, therefore it is 10.
So sine = O/H
Opposite = 8
Hypotenuse = 10
8/10 simplified is 4/5
The answer is B, 4/5