a$)$ A voltage waveform from a circuit under test, that you are displaying on an oscilloscope, looks as follows:

You know that the signal takes the following form:

Taking measurements from the oscilloscope display above, determine $V_p,f,$ and $\frac{O}{?},$ and insert those values into the above equation.

Now rearrange your new equation to make the time $t,$ the subject of this formula and hence determine, to within $3$ decimal places, the first point in time when the voltage waveform has a magnitude of $5\mathrm{.}25$ volts.