In the formula $A(t)=P\left(1+\frac{r}{n}\right)^{n \pi}$ for compound interest the letters $P, r, n,$ and $t$ stand for _____, ______, ______, and ______,respectively, and $A(t)$ stands for ______. So if $\$ 100$ is invested at an interest rate of 6$\%$ compounded quarterly, then the amount after 2 years is ______.