Answer
$\dfrac{1}{\pi}$
Work Step by Step
From part (a), we have:
$y=\sqrt {(1/3)^2+(1/4)^2} \sin 2t+\arctan \dfrac{1/4}{1/3}$
This implies that $y=\dfrac{5}{12}\sin 2t+0.6435$
The amplitude is the absolute value of the coefficient of a trigonometric function.
Thus, we have: $Amplitude=|\dfrac{5}{12}|=\dfrac{5}{12}$
Now, $Frequency=\dfrac{2}{2\pi}=\dfrac{1}{\pi}$
