$7\mathrm{.}1$ Express the current waveform i$($t$)=0\mathrm{.}2$cos$(6$ $109$ t $+60)$ mA in standard cosine form and then determine the following: $($a$)$ Its amplitude, frequency, and phase angle. $($b$)$ i$($t$)$ at t $=0\mathrm{.}1$ ns