If you type sin 53.1 = on a scientific calculator you will get 0.799684658
This is 0.800 rounded to 3 decimal places.
You can use the ratio of O ÷ H to calculate O.
O ÷ H = 0.8
O ÷ 10 = 0.8
O = 8
If you know the value of O and H like in the example below but don’t know the value of the angle then you can get this from a scientific calculator.
For example if O ÷ H = 0.8, you can look up the angle using your calculator by using the inverse sin button (sin-¹). This button gives the angle for the corresponding ratio of the opposite to the hypotenuse (O ÷ H)
θ = 53.1°