$3.[4$ pts$]$ A long solenoid $($n $=1500\mathrm{.}0$ turns$/$m$)$ has a cross$-$sectional area of $0\mathrm{.}400$ m$*$ and a

current given by $1=(4\mathrm{.}00+3\mathrm{.}00$t$?)$A$,$ where t is in seconds. A flat circular coil $($N $=300\mathrm{.}0$

turns$)$ with a cross$-$sectional area of $0\mathrm{.}150$ m$\text{'}$ is inside and coaxial with the solenoid.

a$.[1$ pt$]$ What is the initial magnetic flux through the solenoid?