Answer
$i(t) = 8*cos(250*(2*\pi)t- \frac{3\pi}{4}) mA$
$I(wt) = 8*e^{-j\frac{3\pi}{4}} $
Work Step by Step
Start by finding the amplitude, frequency, and phase shift
By looking at the graph
$A = 8mA$
$T = 4ms$
$\phi = \frac{-3\pi}{4} $
$f = 1/T = 250 rad/sec$
so...
$i(t) = 8*cos(250*(2*\pi)t- \frac{3\pi}{4}) mA$
Then converting to phasor notation
$I(wt) = 8*e^{-j\frac{3\pi}{4}} $
