Here the base angle given is 51°.
The side opposite to 51° is y
The hypotenuse is given as 12.
The trigonometric ratio associating opposite & hypotenuse is sin
We know sin = Opposite/ Hypotenuse
Substituting the values of angle , opposite & hypotenuse
We have
y/12 = sin 51°
Multiplying both sides by 12 we get
y=12 × sin 51°
y = 9.326
Rounding to the nearest hundredths we get
y = 9.33